He accidentally put them under his Servitude/Enslavement skill ( or rather, when they beg him to help them out)
So they're stuck acting like automatic NPC following him for a while, until he run into the Class Prez's group and she manage to cancel the effect on them somehow.
Then when he talked to Prez about wanting to go to his home, all the girls followed cuz home + kitchen + toilet, etc.
(No, they're not his harem of slaves this time)