The article is also entirely about how the PC is a general-purpose register on 32-bit ARM machines. No idea if the 1st gen iPhones or whatever used an idiosyncratic calling convention...but it's moot in the context of this post, because argument passing isn't covered here!

This post really is just about the observation that the PC is a GPR implies that there's a bunch of different ways to get data into it. It's pretty airy. The author was admittedly a first or second year university student at the time, so it's hard to be too mad though.