You will call them. Maybe I'm sounding kind of authoritive here, but seriously. You will, you must, you shall, I'm telling you.
If you don't, you'll just think back at the opportunity and feel bad about not taking the chance.
Sure it might end up bad, but on the other hand, it might end up
really, really well. At this point there are no all too negative signs. They weren't laughing were they? And hell if they are playing a prank, so what. What kind of lame prank is that? And why do it to a complete stranger? A classmate I could sort of understand. No man, they're 99% likely to be interested. Be flattered.