I remember reading that the acronym 'PC' was registered with a copyright, or similar, by a computer magazine journalist, specifically referring to x86 architecture personal computers (termed IBM compatible PC's at the time). Don't know why he did that. Maybe trying to make a dollar. That was all long ago, so the recollection may be off. I have seen the same story written online, as well, but that doesn't really mean much.
Anyway, it's all a bit silly, isn't it? Not a very interesting argument. The undeniable fact remains that when the majority of people say PC in this context, they are refering to x86 architecture.
