The way I understand his idea is that a phone is a general purpose computer. If Apple wants to patent slide-to-unlock, they can only patent a hardware implement

The way I understand his idea is that a phone is a general purpose computer. If Apple wants to patent slide-to-unlock, they can only patent a hardware implementation (i.e. a chip that only does slide-to-unlock, which is clearly a ridiculous idea). Then I can come along and write software for Android that implements slide-to-unlock, and I am not infringing because my implementation is software only. The end result of this means that Apple's slide-to-unlock patent would become worthless.