Watch how this guy reacts to a girl wearing a Hijab verses a girl not wearing a Hijab.
I'm a muslim who doesn't wear a hijab, and I get asked out on a fairly regular basis like any other girl - if I wore a hijab it would be a different story, The reason a girl wears a hijab means she's conservative…and it implies that she isn't the type of girl who would sleep with a stranger, let alone a stranger who isn't muslim. And guys at university, especially non-muslim frat boys are after sex, The second girl just gave a different impression.
They should have tested it on how other girls react from different social circles, because friendship is more based on personality matchmaking - that would be a more reliable experiment.
OR they could have gotten the same girl to go around to different boys, one time with a hijab, and one time without. You would see she would get completely different responses, since she is actually quite a beautiful girl. It has nothing to do with racism, just with what the hijab implies.