PC is the term IBM used for their very successful microcomputer in 1981. For that point on, the term PC meant IBM PC compatible. In fact, PC Compatible was a very common term.
The term to describe smaller computers up to that time was "microcomputer", or "micro". PC meant something specific.
Whether you consider the Mac a PC should be based entirely on whether it runs PC Compatible software, not if it's a microcomputer. I realize the younger generation doesn't know this stuff, and it's confusing, but that's traditionally the boundary between a PC and other microcomputers (which everything is now, since everything uses a microprocessor).