ai poor horse. What you say could be possible, but it is hard to say on paper. We weren't there
I would say wait one or a few more days and wait if you see any differeces during walking straight, in a circle and some short turnings. If you dont see any reaction it will be fine.
it can be sensitive, when you fall on your knees you will feel it too, and you can walk a bit more slowly and stiff, so the horse can do the same.
When he felt very hard the ischium can be very sore. That is a bone which come on the ground when the horse sit on his but. The muscles around that place can be hurt.
Give a lot of love and a soft massage. He will show you if it is okay or not.