i have no idea on why would he be bashir.
I guess their line of argument is that he looks a lot like Alexander Siddig AND that he's wearing (a variation of) a Starfleet uniform (at first). I've seen people ranting "Bashir is a doctor and not a psychiatrist, these people HAVE NO IDEA ABOUT STAR TREK, WHO WRITES THIS CRAP". They will use literally ANYTHING to hate on the show. It's an obsession by now.