I would expect a recruiter for one of the biggest tech companies in the world to have at least some basic understanding/idea of even what linux is - that's not a big ask at all.

Moreover, if I'm a recruiter, unless I'm a domain expert, looking to hire someone into the field and they say they already have it on their resume, I'm going to go and double check their resume and double check my own understanding before I go any further to avoid issues like this.

The only person who looks bad here is the recruiter, and it's entirely their own fault.

The recruiter needn't even be a person. A blind monkey can detect that "UNIX" doesn't match "Linux and UNIX-Like" and reject an application. Pure text matching. Recruiter literally doesn't even need to know how to read.

Most people can't communicate with blind monkeys though, so I wouldn't fault anyone for failing here either.

I would assume at this point that this is some advanced AI experiment Facebook was running to interact with future employees.