Calculating Real Budget Deficit, given Nominal Deficit and Inflation
Edit: based on the video I get the logic that the person was trying to get across. 

Basically the argument is that if in year $t$ deficit was 100mil but the same year the total debt 5billion and inflation was 10% that means that in real terms the value of debt is 500mill less and the teacher of that course treats this as 500mill revenue so under that definition even though you had 100mill deficit you would end up with 400mill surplus because thanks to inflation the net real debt decreased. 

However, I must say it’s quite unusual to define real deficits in this way (see Barro’s Macroeconomics).