Pedantic is very commonplace over in BSD land. So many threads on the mailng list ... of course, you all would know, too: here it's 'Perl vs. PHP', "ASP vs. PHP", "CF vs. PHP", "Hulk Hogan and Andre the Giant vs. PHP".....
Over there, it's "Linux vs. FreeBSD" .....
They aren't the same, true enough. They are similar --- both are 'Unix Like" operating systems. The two (m/l) branches of "Unix Like" systems are BSD and Sys V --- and supposedly Sys V is where Linux got a lot of his inspiration. (Of course, he really had been reading Minix source, IIRC). Incidentally, neither of them can be correctly called UNIX --- they've neither one paid their dues to the authority that licenses that name.
Their pedigrees diverged in 1978 - their last common ancestor was 6th Edition UNIX.
Peter Salus "A Quarter Century of UNIX" has "January 1979" for Seventh Edition, if you really want to be pedantic. 😉 Sixth Edition was May of 1975 (same source). Of course, you've been reading the commit logs and note that it was really before Christmas Break, eh? 😃