[tristor]

The reason you're getting downvoted is because you're saying he's incorrect by making a distinction between UNIX (uppercase) and Unix when referring to commercial OSes. There is no such distinction. UNIX is a trademark for the Unix family of operating systems. All of the systems you referenced as a family of Unix systems are certified and therefore can be referred to in the trademarked way as UNIX.

The candidate is incorrect in his belief that nobody uses UNIX (or Unix) in 2017 and he could have been less flippant in his responses to the recruiter, but his technical accuracy is spot on.

Regarding the minimal distinction that exists, FreeBSD is Unix, but not UNIX, because it has never been certified as there is a cost associated but it is directly derived from AT&T Unix in its lineage. Mac OS X which is derived from FreeBSD in turn was certified and is therefore a UNIX, ironically enough.