He is probably uncomfortable from them digging out the stools - so he's going to act a little off and sit funny for a couple of days.
Does he like the hairball med? It's basically a lubricant to move things along. My cats go NUTS for coconut oil - the solid kind. I give them a glop once a week or so. Mayo is another oily 'treat' that he might like. Anything that he can eat every day - maybe with his food - to keep things moving. Like others have suggested, will he eat his dry food if it's soaked in something like broth or tuna juice? What about scrambled, or raw egg?
Have you tried bits of chicken? Maybe a 'real food' diet for a couple of weeks - or as a daily supplement to his dry food - until he gets this out of his system?
He's gorgeous! I hope he is feeling better soon.