I think, I don't see there the "proving backwards" trick described. The technique goes as follows: a student starts with something (for example, an equation) they need to prove, and transforms it until they get some trivial identity like 1=1.

If they succeed in this procedure, they claim that the original equation they started with was correct too.

Everyone does it, and it takes ages to make them unlearn it.

If somebody is wondering why the technique is incorrect: starting from a false premise, any statement can be proven, including things like 1=1 or 1=0.