(Regardless of more positive information given in the three links just ninjaed, (and the fourth ninja just happened, post-pre-post-edit) here's my version of the reply.)
edit: Of course, on checking, the link-replies did not directly ninja me, it turns out. Though Patrik summarises what I say very well indeed. . Still, the subforum pointed to is good to know of, the Wikilink has loads of Food info and if you can help indicate where you're going wrong (as an uninformed new player, once you have become informed enough to know where that was) your input in that thread might be invaluble.I used to get "Urist McHunter cancels hunting: (because they are now) Hunting for vermin" a lot. Hence the forum name.
i.e. I'd done such a bad job of feeding the (whole) fortress that even my hunter had found themselves beyond being able to produce anything quickly enough. The desperation drags them away from (the initial stage of one form of) food production.
Obviously, it seems your example is not suffering from total lack of food, fortresswide. And hunger will override/ignore Burrow limitations, and I'm fairly sure even military service (as might be applicable). It's been so long since I've needed anything other than drink-giving (I sometimes have miners get thirsty when restricted to a priority job area by burrow that another dwarf goes and 'waters' them, though full dehydration should cause them to break off) that I'm not certain that available food is similarly given under such circumstances, but I'm sure it is. And if all food is 'owned' by someone else then this won't be your only unfortunate, even if he's the worst.
So we're probably talking
physical separation from your food-stocks, and anyone who has access to those stocks.
Have you drawn up your drawbridges/locked the entry-doors/walled off the entry+exit corridor/accidentally deramped a vital pathing-ramp? Check for that (maybe try to use a random but identifiable stone inside your fortress as a material in building a prospective wall right next to where Commander McHungry currently is?) and remove the cause immediately if that's the case. If it's that he
should head off to food (or maybe the reverse).
You could also set up a food (prepare meal) stockpile next to him, in case that snaps him out of the vermin-hunting, but you don't get the immediate "that aint gonna happen", and forcing the food movement is not going to help on its own (especially as it's not really abailable while being hauled).
If there are other issues, we can look for them after ruling out the above, though.