"They will act differently with you if they like you" - Ok but the mixed signals!??!

He's usually the social type around people he's comfortable with, likes to joke around and laugh. But when he's with me, not around his friends, he goes kind of quiet and non-chalant... Like I was telling him about somwthing I saw as I walked past him and he just went "Oh, cool". Later I asked him a question and he went "hmm, I'm not sure." Recently too when he has more direct attention on me he generally is very "eh" feelings. But get this...

When I come up to greet him he lights up with a big smile and says my name, and when he sees me out and about he'll do his usual "Oh, hi [name]!" All enthusiastically. I get butterflies when that happens, like is he happy to see me?? But why does he treat me so passively otherwise 😭

Would love some insight...