In the era under discussion, a "PC" was _by definition_ a computer with an x86 processor, and Macs and Amigas and Ataris were Something Else for boutique users.
"The designation "PC", as used in much of personal computer history, has not meant "personal computer" generally, but rather an x86 computer capable of running the same software that a contemporary IBM PC could.":
https://archive.org/details/byte-magazine-1977-05/page/n35/m...