Countries like the DPRK and others joined the Non-Aligned movement despite showing clear proofs of support towards power blocs were and still are a part of the Non-aligned movement. During the Korean war, the PRC and the USSR clearly showed support towards the DPRK which was greatly accepted by the DPRK. After the war, it is said that the DPRK got nuclear support from USSR which very clearly shows that the DPRK was aligned with the USSR.
According to John Lewis Gaddis in his book The Cold War:
Non-alignment was "a way in which the leaders of the 'third world' states could tilt without toppling: the idea was to commit to neither side in the Cold War, but to leave open the possibility of such commitment. That way, if pressure from one superpower became too great, a smaller power could defend itself by threatening to align with the other superpower."
Essentially, smaller states joined this movement seeking gains for themselves such as ones economically and militarily. Whilst they seemed "clearly aligned" to one superpower, they were not really loyal to them. West European countries only allied with the USA as it was an industrial powerhouse, and Communist countries such as China formed close relations with the USSR for trade and technology (e.g. atomic bomb). However, as these states were weaker, the superpowers often demanded things from them, such as change in government systems, denying trade with the "other side", etc, limiting their freedoms and economic growth, hence motivating them to strike a balance between the two superpowers to avoid over-reliance on either one. Other examples:
Tito and Yugoslavia: (pioneer of the movement, "clearly" aligned to USSR)
Tito sought to remain independent from Stalin and the USSR. He had conducted his own Communist revolution without Soviet aid and so had no reliance on Moscow to maintain his power. However, Stalin wanted to unite Eastern Europe under his orthodox ideology, i.e. domination over them for industrial production and more. When he publicly broke off relations with Moscow in June 1948, Stalin claimed "I will shake my little finger, and there will be no more Tito." Literally, Tito had reason to be cautious as Soviet assassins were sent to kill him (but all failed); Yugoslavia was also in a precarious position economically – she was denied the subsidies that the USSR provided Eastern European countries with to rebuild their countries, tarnished in WW2. Thus, Tito reached out the USA and received Marshall Plan economic assistance. Buildup of forces in neighbouring countries like Hungary also threatened war with the USSR, so Tito hoped that his ties with the USA would deter war as the USA may also become involved, causing a "hot war". Tito later initiated the Bandung conference of April 1955, joined by Zhou Enlai of the PRC and Jawaharlal Nehru of India, which historians mark as the beginning of "non-alignment".
North Korea - DPRK Unlike Yugoslavia and PRC, North Korea relied on other Communist countries for its establishment (PRC and USSR), so/and it was weak politically and militarily, only joining the movement in 1975-6. I do not usually take an intentionalist stance, but here it appears Kim Il-Sung was pretty independent from the start, and had his own agenda despite having to rely on other states to achieve them. Before the Korean War, Stalin initially believed it was unwise to invade the South, and implied that the USSR would not readily give him aid, asking him to talk to Mao. In negotiations with Mao, Kim was not explicit with what Stalin told him, and portrayed the Soviets to be more battle-ready than they really were. Then, in talks with Stalin again, he also portrayed Mao similarly, convincing both states to aid him in the war. Bruce Cumings says that USSR control over DPRK was "flimsy" and she was not solely reliant on Soviet arms – my point is DPRK was never really "clearly" aligned with the USSR in the first place. Also, you say that DPRK got "nuclear support" from the USSR (which is vague - what is nuclear support? technological aid? sending them nukes?). I have not read about this, but even if this happened, it does not necessarily mean North Korea was "clearly" aligned with the USSR.
Take Mao's China for example. He convinced Khrushchev to send specialists to help China develop its own nuclear arsenal, but Khrushchev only relented under the condition that he had full control over its use. (Of course, Mao wanted nuclear weapons for his own. The later Sino-Soviet split around 1969 suggests that this "alignment" to a superpower and having to bow to its wishes fueled a state's desire for non-alignment) The worsening of Sino-Soviet relations ended in Soviet withdrawal of nuclear cooperation in 1959. So offering of nuclear technology cannot clearly define alignment.
Furthermore, North Korea was a bit different from the rest of the non-alignment movement as it didn't threaten to defect to the USA (which is a show of her own strength), rather it claimed it was weak. Whenever the Soviet leaders suggested reform (i.e. solidarity/conformity with the USSR), Kim would counter them by claiming they would destabilize his government, thereby handing victory to the South Koreans and Americans. Curiously, this was the similar case for South Korea and the USA. Syngman Rhee "blackmailed" Washington into a bilateral security treaty, along with US commitment to keep American troops in South Korea for as long as they were needed to ensure her safety. The USA did the above despite Rhee releasing thousands of North Koreans POWs so they could not be sent home against their will, which was a post-war agreement, enraging both North Koreans and the USA, threatening the collapse of the armistice. As Gaddis said: "being a dependent ally would not necessarily make [Rhee] an obedient ally."
I realize I have gone on quite a bit, and some of the above focused more on taking your question apart. Most of the evidence came from Gaddis, but I am happy to clarify on my rambling.
- Western observers often overlooked the splits in the Communist bloc. The differences between China and the Soviet Union were hard to ignore, but there was Yugoslavia, Albania (at times), and also the DPRK that were not entirely aligned with Moscow.
- Other countries like Chile, Panama or Peru joined despite being kind of Western.
For people who grew up in the trenches of the Cold War, or whose history teachers did, it was "with me or against me." The countries of the non-aligned movement wanted to trade with both sides.