I have it he was hurt pretty bad. The first standing 8 was as legit as you can get without going down his head almost turned around exorcist style and he would have gone down the second time had it not been for the ropes. If the ref let it continue it would have been ugly. I'll upload it later. Against Medzhidov his legs buckled, stiffened or turned to noodles literally 10 times during the fight. That seems to happen when he gets caught clean but he does appear to recover reasonably quick.
You don't need to be hurt in amateur boxing for them to stop the fights, nothin to do with Joshuas chin. There would be outrage if most of the amateur stoppages happened in the pros, you can be stopped for just taking a few heavy looking shots even if they aren't affecting you.