Which error is this?

[Rev. Rye]

I suspected that a false premise was the problem here, but, somehow, I had to ask myself “surely that’s not the sole problem here. There has to be a more fundamental problem here.” Unfortunately, it may actually just be that simple. Maybe that’s why the closest thing I could find to an example is ‘an inverted modus tollens.’ The logic itself is sound. The initial premise, however, is invalid and easily deniable.