you can call it like his fixed or go-to facial expression. his smiles mean anything, everything or nothing at all. he cannot understand the concept of emotion
Ah I see, I thought he figured out Dane is the omega he was looking for during their fight and that's why he is happy
that will be a bit of spoiler if you read this without being a novel reader sorry
It's js the way the artist drew it, the novel didn't mention him blushing like that, he was more pissed.
Why is he so happy after he got beaten up like that ヾ(❀╹◡╹)ﾉ~