The general popular idea that the quote in question appears to be trying to counter is that the northern barrier of the Himalayas made the subcontinent nearly immune to invasion, and thus utterly cut off from the rest of the world. Particularly from powerful neighbors on the Asian steppe, who were militarily difficult to cope with until the invention of gunpowder.
Since the northern border was effectively militarily impassible (to non-Tibetans anyway) and the eastern largely jungle (which isn't much better), nearly all historical invasions of India came from the northwest (modern Afghanistan, which is also mountainous too), or in later years ship-borne carried by the monsoon winds.
It was in fact successfully invaded by the Mughals, and earlier by Indo-Iranian steppe people*. However, India didn't suffer invasion from the Huns that we know of, and is certainly better equipped with natural barriers than Europe, where the Huns got nearly to the coast of France before being pushed back. It successfully staved off invasions from both the Greek and the Mongol empires at the height of their powers.
So yeah, it wasn't totally isolated and impregnable, but it also wasn't nearly as vulnerable as China, the Near East, or eastern Europe.
* - We don't have a great historical record for this, so we don't know much about the nature of this movement, other than that it happened. Some people hotly push back on calling it an "invasion", either for that reason or for personal political reasons. So be careful about using "the I-word" in mixed company.