Missed this comment earlier, but yes, it does feel like a bit of stretch that these characters will all just happen to be in the library at the exact same time and that they would be convinced to play the game. The MC and Jill have played before but it didn't seem like the MC was all that keen to do it again, and I can't really see M&J being interested, especially Josy, even if they're in a relationship with the MC.
The MC dreaming about these LIs in this scenario therefore seems like a very plausible possibility.
That's what I'm thinking.

This just looks like such dream material with 3 LIs and Sally in this fantasy environment that I can imagine DPC doing this just to throw in an all-girl orgy with characters who won't do this sort of thing in the MC's real world. And either it will be a nice wet dream for the MC, or it will turn into a nightmare when he goes to join in but then looks down and finds he has no cock.