While their was no blanket push to saddle the South with the Unions war debt; that could be an interpretation of what happened. The CSA debt/burden was larger than the Unions, and mostly held by southerners was not assumed by the North. The Unions debt, largely held by northerners took more than 30 years to entirely repay and the South re-incorporated in the Union did pay a proportion of that debt as part of the newly reunified United States.
To give your buddy the benefit of the doubt. The Union did refuse to assist the Confederate States with their war debt. The Union further refused to pay reparations for slaves freed. Also of course the Union refused to cover any of the former CSA's war debt all of which were significant hits to the former Confederate States and the citizens in those states who financed the insurection. Furthermore as the former confederate states were reincorporated into the Union, they did participate in paying for the Unions debt, as it took 30+ years for the Union to pay down their debt and all that time former Confederate states were contributing to the federal income. So while I would say your buddy was mostly wrong, I could see how such a claim might be justified.
While it's arguable not accurate, what is accurate is the citizens of the insurrection states who financed succession paid a huge financial burden.
War Debt was the political football which the North and South kicked around for years following the Civil war. I think your friend was mistaken about the Union saddling the south with it's war debt suggesting the northern States didn't share in the burden.
In the years following the Civil war the South was bankrupt. It's industry and farms were unserviceable and their credit was depleted. Making the South pay unilaterally for the Norths debt would have been the same as defaulting. It was not an option. The Union was much more concerned with the "repudiation crisis" / scenario.
below based on Repudiation! The Crisis of United States Civil War Debt, 1865-1870
In the Constitution slaves counted for 3/5ths a person for the purposes of representatives in congress. When the Union passed the 14th amendment the fear was they had just handed the South a huge increase in congressional votes. Which according to the fear of the day could be used by the south to (1) cause the Union to default on it's war debt. or (2) make the Union assume the confederate war debt. This fear and what occurred in the name of that fear is called the "Repudiation Crisis of 1865".
Both the North and South had significant war debt. The Unions debt had raised from $65 million dollars in 1860 to 2.7 Billion in June of 1865.
debt per capita had increased from $2.06 in 1860 to $75.01 in 1865.
The South had even more debt. Individual Confederate States owed 67 million dollars. The CSA owed about 1.4 billion. Compensation for freed slaves in 1860 amounted towards 1.7 billion, ( which the Union feared might be the price of peace).
The North feared since there was no Constitutional amendment which said the US couldn't repudiate it's debt, the South would try to make the Union default as the CSA had defaulted. Union debt was mostly held by Northern Investors. To make matters worse the Secretary of Treasury Simon Chase, thinking the war would be a short war, had the majority of the Unions debt in short term vehicles which needed to be paid or refinanced. Refinancing that debt would require congressional approval.
In 1868 there was a further Repayment Crisis (The Ohio Idea) over whether Union Debt should be paid in greenbacks or gold. The US had gone off the gold standard during the Civil war, and issued script called the greenback. After the war the greenback was trading below gold values. So paying the debt in devalued script was a mini repudiation strategy proposed by several Southern sympathizers including then President Andrew Johnson. Hence the 14th amendment to the Constitution which took effect in 1868 contained a section on civil war debt.
The Fourteenth Amendment of the Constitution
Section 4. The validity of the public debt of the United States, authorized by law, including debts incurred for payment of pensions and bounties for services in suppressing insurrection or rebellion, shall not be questioned. But neither the United States nor any State shall assume or pay any debt or obligation incurred in aid of insurrection or rebellion against the United States, or any claim for the loss or emancipation of any slave; but all such debts, obligations and claims shall be held illegal and void.
The repayment crisis wouldn't be resolved until President Grant would take office.
In 1870 President Grant's Secretary of the Treasury Boutwell finally got a strategy through congress to retire ( refinance ) the nations Civil war Debt. Congress authorized the Secretary, to issue $500 million in 10 year bonds at 5 percent, $300 million in 15 year bonds at 4.5 percent, and $1 billion in 30 year bonds at 4 percent. These bonds were to be paid in gold and exempt from local and Federal taxation. Though it would require more than 30 years from the end of the war for the Union to pay off it's Civil War Debt, the 1870 act closed the book on the repayment and refunding crisis which followed the war.