The recruiter handled himself professionally and should be commended for not being bullied. Mr. Zhang sounds like a punk, and would probably be better served by pulling the image.
Especially since this is a UX research internship, and the candidate made perfectly clear that that is how the recruiter was coming across, so the recruiter had every opportunity to clarify.
The candidate didn't handle it perfectly, the recruiter however handled it far worse.
Early phases of job applications are about following directions and saying what you need to truthfully say. I'm actually surprised that my original comment was voted into oblivion -- its a pretty obvious reality. The recruiter did his best to say "Just write Unix" without crossing a line.