
Some people aren't trying to understand the leader, yes he did reacted harshly and he could've acted better but try to look at it in his perspective, it really is kinda weird to read a fanfic about you and your friend (even if it's a man, woman, non-binary), even idols feel that, it's a slap in the face that some idols does act like that towards fanfics that not every idol is comfortable with it, that's why fandoms collectively agrees to not mention any ships towards groups.
He didn't like it not because the other was a man, he's bothered by it cause it's his FRIEND, and did they show what the fanfic is? No? Then as far we know it could've been a smut fanfic

It's kinda like http://www.mangago.zone/read-manga/ecchi_suru_nara_papa_ana_de/ but make it bestiality
I didn't really get it but atleast he's happy