Well, in the sense that the Mac is a Personal Computer you are right, it is a PC. However, since the generally accepted 'definition' for a PC is something that runs Windows, then a Mac is not a PC, in that its original purpose is not to run Windows, but to run OS X regardless of whether or not the system is capable of running Windows.
So, you are still technically correct. However, perhaps you should learn to be a little less anal before you correct someone for 'misinformation'
Perhaps he should have written "A Mac is not a Wintel machine." Although even this is a half truth, because through Bootcamp, Macs are Wintel machines
Seriously though, the important thing to remember is, Apple does things differently, and in this case, I happen to like Apple's way of doing things. In other ways the Wintel industry (the real one, not the pseudo one we can claim via Bootcamp) does things better.
Either way, cool yourself. A simple correction would have sufficed; you don't need to flog him
