Teen thumb sucking

My son is 15 and I didn't actually raise him... My mom did. I had him at 15 then left to live with my dad because my dad was much more lenient and let left my son with my mom. I showed up a few times a year and did send him birthday and Christmas presents. He called my mom, Ma. Me and my son were honestly more like siblings than anything. My mother passed away so my back in April and my kid lives with me my boyfriend. I never knew this but I guess my mom failed to break his thumb sucking habit like 13 years ago 🙄. Whenever he gets upset he sucks his thumb and I told him he's too old to be doing that. Yesterday I was going through pictures of mom and IG that made him upset because he started thumb sucking again and I asked him "Do you want a binkie?" He got sooo offended when I said that. I mean, if you're gonna suck your thumb, might as well suck on a binkie since that's supposed to be better😂. But I doubt anyone has ever dealt with this and I just have a weird kid, but just Incase anyone know what I'm supposed to do about it?

Edit: I wouldn't say I was necessarily being mean or anything. I mean aren't binkies supposed to be better than thumb sucking lol?