Interesting discussion! Here is my take:
So I would look like a sore thumb in the society if I said that Macs are PCs?
Language is a living thing and how people use language evolves constantly.
There are many examples for technically wrong words or phrases that are used everyday.
Just a few:
"ATM machine" (the M is redundant), "PIN number",
"added bonus" (a bonus is always something extra), "personal opinion" (an opinion is always personal),
"chai tea" (chai means tea in other languages),
"i literally died laughing" ("literally" used incorrectly)
While you are technically correct that a Mac is a personal computer, the term "PC" is no longer used in that sense. Consider other words that have changed their meaning over time. "Gay" is just one prominent example.
In other words:
I don’t like the term *PC* when people use it to refer a non-Mac since it stands for *Personal Computer*.
The term "PC" is no longer understood as an abbreviation of "personal computer", but a synomyn of a "computer running Windows".