He would've had to cook the rice from scratch instead of just reheating it (if that's even necessary, the item box probably locks things in the state they were in when you put them in it). You don't really feel like cooking another thing while you're already eating the first. Next time he'll just have to remember to keep rice in stock ahead of time so it's not an issue.
@Karikko They don't, certain animals will consume grass and similar things to deal with stomach problems (like dogs), but overall most carnivores only eat meat. To the point that some of them like the Komodo Dragon (which is fine eating rotting bones) will not eat the stomach of its' prey because it had leaf matter inside of it.
Wolves are carnivores, stupid protagonist. Of course he wants to eat meat. You can't just feed him a human diet and expect everything to be fine. What an imbecile.