exactly what did he mean by this?
Most Helpful Guy
Well, a B is a good grade, but the guy should have kept his mouth shut.
If you're only a friend, the guy would probably never tell you if he thought you were more than a B.
So this can roughly be translated as him saying, "I find you attractive, but that doesn't mean I'm hot for you."
On the other hand, if a guy told you were anything less than a B, it would be a total insult and I don't think this guy is that stupid.
So ultimately, it pretty much means absolutely nothing, or close to nothing. He probably just said it to see how you would react.