Brother is implying he has a fetish, but we don't currently know. The brief lil flashback we get in some other chapter seems to imply the situation is more like he got his heartbroken by a hybrid once and has been chasing a relationship like that since then. But he definitely looks like a chaser rn.
They are "assuming" it a fetish based on the limited information they have and we are doing the same thing. We can only make inferences not cast judgement. Dallae is insecure about this and his brother is using his insecurities to get what he wants. Whether his intentions are good or not. Mr. Kang has to communicate his insecurities and past with Dallae, yes but he can't be forced. I'm not saying it looks good on Mr.Kang's part, I'm just saying we can't throw judgement and assumption without all the information. The comment about the "type" was a sarcastic joke.
im sorry, maybe its my bad for being as cynical as the brother but i think for this he's in the right to look at it and be like "thats weird" n show dallae. The same way we cant judge that mr kang is a chaser i feel we shouldn't just assume anything the brother does is meant to be controlling, esp when we agree what hes talking abt is indeed shady
n ig my fault for not assuming the type thing is a joke or sumn when like so many ppl in the comment section genuinely say that

Good forbidden somebody has a type. Also big bro is using manipulation as "concern". "I do all these things for you, so you HAVE TO do as I say".