Was he flirting? or am i just paranoid?

i was in a theater class, nothing was going on, there was music playing, some people were dancing...and then this guy grabs me around the waist and starts ballroom dancing with me....i'm not exactly cute, so i dont think he was flirting, but it really caught me off guard. i see him every day, he is in a few of my classes...and he talks to me more often lately....i'm not really sure what to think of it.