This is odd to med.
He is just going and staying 1 1/2 hour? twice a week? Isn't he going every day so he can get used to it? Are you staying too He isn't getting the chance to adapt to anything. He goes home and has a different routine then goes again. This would be hard on a child going this schedule for anything.
I would say unless you can take him more hours and leave him for several more hours each day he is going to take a lot longer to adapt. He has no sense of the routine. He is not even going through one period of the day. He is not getting play time, learning time, nap time, lunch, snack time, finger painting with jello time, he has no idea it is a fun place to be since he is not there long enough to experience it.
I would tell you, if I were the director, that he needs to come every day early in the morning, when class time starts. Then he needs to stay until at least lunch is over.
This way he gets to acclimatize and learn the routines. He gets to see the other kids playing and see the teachers interact with the kids. He gets to find a home and stop being visitor.