The student is representing only himself. The recruiter is representing the company.
When a recruiter mishandles a situation so massively as was the case here, it puts Facebook in a poor light. Obviously, Facebook's engineering teams are well aware of what all of this technology is, but it is distasteful to see this complete lack of understanding and know that I might have to deal with it if I were to work with one of their recruiters.
I'm not saying the industry in general is better than this, but it would have taken the recruiter all of 30 seconds to draft an email to the hiring manager and ask for clarification - "This guy is really insistent on how he has POSIX and Linux experience and that this will be okay. What do?"
Also, putting Unix on the required skills for an intern position? What did they think was going to happen?