I agree with your agreement in principle, but the real mistake was not simply adding Unix to the skills list to begin with, and keeping POSIX and Linux. It's not really a lie, and it's pretty obvious from the first email what's going on with this recruiter. Besides, if he's touched a Macbook, he's used UNIX in some form, because at least 7 versions of OSX have been certified as Unix [0].
I don't think I'd have thought of one ignorant recruiter out of a company of many thousands as a red flag. We have a great recruiter at my company, but I have no idea if he knows the difference between Unix, POSIX, and Linux, or if he knows OSX is a Unix (tm).
I don't see a recruiter not knowing the particulars of POSIX/UNIX differences as the red flag (heck, I'm not even sure I could answer that question). The red flag to me is that the Kafkaesque exchange that followed, I suspect, is the product of the overall recruiting culture rather than a lone recruiter.
Oh, right, the "deleted Linux -> we need people with Linux experience" bit is pretty stupid. Still, I'd probably chalk that up to one ignorant recruiter and just put all those words on the résumé to satisfy them.
I don't think I'd have thought of one ignorant recruiter out of a company of many thousands as a red flag. We have a great recruiter at my company, but I have no idea if he knows the difference between Unix, POSIX, and Linux, or if he knows OSX is a Unix (tm).
[0]: https://unix.stackexchange.com/questions/1489/is-mac-os-x-un...