Given that he's had some ear infections, it might be a good idea to ask for a referral to get some specialist hearing testing and maybe a check with an ear nose throat person if there's any sign that there might still be a problem. If his hearing is muffled in other ways, then it would be a bit like the noise you get when you're underwater and you hit your head (kwim?). I'd be following up on this because hearing is so important for speech development, you don't want to take any chances with it.