I mean, for once, I totally agree with the girls getting hysterically mad at that. Especially Pyeii. Our dumbass MC doesn't realize that the way he introduced them leaves the smallest of connections between him and them. Hell, Pyeii isn't even a sister but just a friend of a sister which is basically just an acquaintance. As for Sung-ui, yeah their relationship isn't much more than what he said but they are getting closer.
So yeah, in all his introduction of them was pretty much terrible.