I can see it a bit?
A party is set up for your group, gender, or culture but then the ensouled-demigod brings her human. Even if Tsukino is chill, Mummy and others get a bit stiff and the whole mood cools. It's not the worst thing the trickster goddess has done but safe space sometimes means keeping the graveyard closed to outsiders.
Luckily most of the attendants don't have enough of a soul for Hinami to give a damn.