Is this cheating

My boyfriend was at a party and got drunk with a girl, she was sat on his lap in a car and was clearly into him and he thought she was pretty. He said she lost interest because he threw up. He was pretty vague about how interested he was in her, or what would have happened had she not lost interest. Nothing happened between them but the whole situation doesn’t sit well with me. I can’t tell if I’m overreacting or if this is a genuine reason to be upset. The whole thing happened a while ago but I just now found out more details about it.