Stupid question, but does he understand the weight of what he did? I say this because I was working on a startup several years back and one day I got chatting

Stupid question, but does he understand the weight of what he did? I say this because I was working on a startup several years back and one day I got chatting with my friend's brother about it. He seemed interested and I suggested he could help out if he wanted. Anyway a few days later I found that he listed himself as a "co-founder" of my startup on Linkedin. I wasn't mad or anything - it was in such early stages it's not like it really mattered. But I spoke to him about it a few days later and he seemed really embarrassed about it and acknowledged he should have asked me first, but explain he was just really excited to be part of it and got carried away. I thought was kinda cool if anything because I sensed he didn't mean any harm by it and he just wanted to put his name to something he was excited about and the "co-founder" title sounds cool to some people. I guess what I'm trying to say is that some people really just like titles and he may not realise why what he is doing is wrong. I'm guessing that's not the case, but worth getting his perspective first maybe? Otherwise I'd echo what others have said here. Seems like a red flag if he understands what he's doing.