
I am confusion at first but I think it all boils down to Minato ending up with the idea that Itsuki would go for guys now too because in chapter 2 they had a talk about doing it just because it feels good. And because Itsuki went to the gay event, he thought his guess was right.
Also proof of this is how in the last panel when Minato was drunk, he began describing wanting to grow out his hair and dye it and other stuff like bigger eyes or whatnot. I thought he was describing a girl, but he was most likely describing "Tama-chan".
(Edit: just read the previous comments and it seems we all have vaguelt the same theories hahahhahaha. GO US!)
Oso: Are you aware of a gag order?
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Guard Bailey: Oooh bitches you would not believe the tea I'm about to spill