how do I know if someone is joking or guninely asking?

I was sitting in the lecture and a dude I know came by and ask me “what group is this? ” with a small laugh I thought he was trolling and wasn’t serious because he’s kind of person who make jokes all the time so I replied with “whatever” and continued to make jokes instead of actually answering the question . After that, he went to another person to find the answer. I know that wasn’t hard to figure out but sometimes is gets really confusing and I reply depends on my mood.