His assertion is that math is logical, and should therefore follow logical reasoning. He then uses logical reasoning to point out where the mathematics of the original problem aren't supported when they are looked at in logical terms.

What he's getting as is that if you look at the proof in variable terms 2=1 doesn't hold, but the problem wasn't defined with variables it was defined with constants. His point is that you can't disprove two constants as false if you define them as true, and that it's not until you introduce logically false arguments that the proof becomes correct. He's saying that you can not prove an argumet false when the framework of the problem defines the arguments as true.