Riley very much enjoyed bowling with her confusing new friend. And having someone to see back-to-back movies with.
She had missed being able to have someone built in to do things with. That had always been one of the best parts of relationships for her. But this wasn't a relationship! Even if Dietrian did hold her hand everywhere they went and comfortingly put a hand on her knee when she got freaked out by the jump scares and mass murder sequence in the first movie.
He was really nice about the whole thing when she was embarrassed afterward. And insisted on paying again for the second movie AND snacks. He had to be rich. He didn't work and could afford to constantly be doing activities and going out to eat.
Riley would have felt burdened by this if not for the fact that he was very obviously benefiting from having someone to do things with too. He really had been lonely, hadn't he?