Xehanort has learned some months ago that he'll never figure out what he does and doesn't like if he doesn't give everything unfamiliar at least one try. The downsides of amnesia: what's obvious to some is a deep and profound mystery to others! Like tastes. So the offered roll is taken, albeit carefully.

And then examined, and then sniffed. "..If mine has anything like that, I haven't seen it." But he's not going to dismiss the possibility! "It is very handy. Can anyone get one of those?" Arms bands, specifically.

Probably no though, he's already figured out the train only offers what someone would normally have access to, and hammerspace isn't one of those things. Experimentally, the sushi roll is bitten into like it was a taquito. It's not instantly revolting, so he keeps going. Mystery food, and it's not loaded with sugar!