Can someone please tell me what is Wooyeon's beef with alphas? Because it doesn't make sen...

I think it's just the way that alphas were the ones bullying him when he was younger.

Iirc, it's because of his mom. She is an asshole.

Well, it wasn't really explained in the novel that well. Wooyeon grew up with these trashy alphas all his life, never treated well by them. Even his own mother is an alpha and he doesn't even like her. Wooyeon is a dominant omega so there's a good chance he was also often bothered by them when he was in states cause that's when he presented as an omega. Later on in the novel, he has a beta friend called Danny which his name does get mentioned a couple of times in the manhwa already. He told dohyun that he taught Wooyeon some self defensive to help him deal with these annoying alphas. Remember that sunbae during the welcome retreat? he scented the cups with his alpha scent. He often was around such trashy alphas. Most alphas are pretty trashy in this bl, with some being actual good. Moon garam and dohyun are actual good alphas and we don't often see alpha's in a good light.

Remember very early on, the girl in their club suddenly acted up after being exposed to the main character omega scent. It's likely that he grew up having to deal with this type of harassment on top of bullying, and there is also his alpha mother. It's likely he has never met a good alpha in his life, hence why he was upset when he found out Dohyun is an alpha and had lied about it.