It is not uncommon to come across open positions that actually do require Unix (not Linux) experience.
For example, American Express has a large deployment of AIX systems and they indeed look for candidates with experience in AIX systems, although I believe someone with experience in another Unix or Unix-like system should also be okay.
But I agree that such openings are usually quite specific about which Unix system they are working with.
This is true, but I would imagine that, if not in the job description, if a really specific kind of Unix experience is required, it would come out in the exchange - and be really OS specific and actually say - True64, AIX, Solaris, etc.
"Unix-like" today means bsd/linux. The recruiter did bad, but recruiters will always do bad.
If its a job you want, don't let a recruiter foible disqualify you, if you can help it.
For example, American Express has a large deployment of AIX systems and they indeed look for candidates with experience in AIX systems, although I believe someone with experience in another Unix or Unix-like system should also be okay.
But I agree that such openings are usually quite specific about which Unix system they are working with.