Factual error: Mulder refers to a Royal Navy vessel that sailed from Leeds. No large ship can sail from there - it is at least 50 miles from the coast.
Factual error: Mulder mentions the USS Eldridge as disappearing from Philadelphia (and later reappearing in Norfolk) "nine months after Roswell", i.e., May 1948. In fact, the supposed incident took place much earlier - in February 1943, according to almost all reliable sources. (00:06:50)
Answer: He was being facetious. He doesn't specifically know that information, he was merely giving examples of the types of information he has access to.
I think so too.
lionhead