Can I ask y'all something? May be a strange question....?

How do you end up with a bruised lip if you haven't bumped or bitten it? I saw my boyfriend on Monday and everything was cool..no bruised lips. Tuesday night, he called me and started an arguement with me; he hung up on me and wouldn't answer the phone for the rest of the night. The next morning, I went over to his place. I wasn't looking for anything, but noticed a bruise on his lip. When I asked him what happened, he gave me a sarcastic comment, "Yeah, somebody bit me on the lip." He then claimed that he didn't know what happened and denied hitting or bumping his lip. After I pointed it out, he DID kind of start acting kind of guilty or something. Of course he refused being with anyone else. Anyway, do y'all think that possibly he got the bruised lip from kissing or putting a hickey on someone? Has anyone ever gotten a bruised lip from kissing or any other ual activity?