Yes, they do sometimes sleep in feeding boxes. I always think of it being like they realised they were out a bit late so just rolled up in the best place to hand – i.e. the feed box! I have had one in one of my feed boxes for a couple of nights a few nights ago, but managed to squeeze the bowl out without disturbing him. He didn’t seem to mind and was back sleeping there again the next night. I suspect it’s the same hog who started building a hibernation nest in another feeding box nearby last night.
If you get the chance, if he vacates again, I would clean the box out, with boiling water (assuming it’s wooden) – they sometimes shed ticks which may produce eggs in the box – even when they have only made short stays.
But, if he starts building a substantial nest in there, I would leave him be and maybe try to leave some food elsewhere.