Why was he-tians "brother mo" so hot??

He probs said something equivalent to hyung, just my guess.

Exactly. He said something much more pleasing to hear, maybe "Mo Gege", its also used as a really flirty gesture, a girl to her crush, a wife to her husband. Also little mo is probably something like "Xiao Mo" its really cute.
Lol can say its equivalent to "daddy" what most people here want Mo to say.