According to the article you linked, that was debated even at the time:
> PC Magazine Editor in Chief Lance Ulanoff criticized the campaign's use of the term "PC" to refer specifically to IBM PC compatible, or Wintel, computers, noting that this usage, though common, is incorrect, as the Macintosh is also a personal computer.
But it's not the PC(the IBM 5150) or one of it's inheritor machines.
To be honest I agree with you, If it is intended as a personal computer it's a PC. Yes tablets and phones(Pocket Computer???) included. But I understand the argument that a PC is a specific architecture. it's a wrong argument, but I get it.