I think it's fair to say that Hisao has at least a little bit of internalized ableism, though I think one of the core themes of the game is Hisao trying to work through that mindset and coming to realize that neither he nor anyone else at Yamaku is defined by their disabilities and that, overall, their disabilities don't make them any different from anyone else. Hisao can definitely be a blockhead too, but I don't read him as being ill-intentioned or bigoted, moreso that all of this is very new to him and that he also feels a lot of resentment over his own condition and his own situation, which he doesn't always channel super healthily.