it depends on how the guy himself looks. I don't expect an ugly guy to be dating anything but an ugly girl so I wouldn't think anything out of the ordinary.
if he's ugly = "how sweet 2 ugly people found love in spite of all odds"
if he's just average/ok looking/nothing special = "its normal, he probably likes her for her"
if he's really cute/good looking/fine = "he's using her for money/taking advantage of her/he beats her in private/there is something seriously wrong with him and she's the only one willing to put up with his sh*t"
I know that beauty is all subjective, so I probably wouldn't think much of it. Maybe I would think that the girl also has a really enticing personality going for her...
But if I heard that the guy was questioning things because he wasn't sure what other people would think, then I would just think he was a total butt head, and that the girl deserved so much better, haha
its a hard thing to speculate. A good person really won't pay attention to looks its more compatibility and what's inside. But I would assume B he is a man with a good heart and knows beauty is only skin deep.
There are many posibilities...She probably has awesome personality or must be rich...Or maybe that guy like to dominate so being with less attractive girl would give him the chance to do so...