Jerry, excellent questions.
First of all, wilderness rangers roam around the Mount Whitney Trail where these two guys were going to be, and they specifically roam around at Trail Camp where most people spend the night. If you have a tent erected and are sitting there, then the ranger might wander up and ask about your stove (whether it is right or wrong). If you suspected that your stove was wrong, you might need to keep it under wraps except for cooking.
Now, Trail Camp is a pretty bleak place. It is far above timberline, and there isn't much of anything that would burn up there. However, rules are rules. I think maybe if you tried to plead ignorance, a nice ranger would simply give you a warning. If you gave him a hard time about it, he could issue a citation or escort you out. Those are kind of unlikely, but possible. That's why they normally ask to see your permit first, since it has all of your identification on it.
I had heard about the approaching fire restrictions, and I was thinking of going backpacking in the Ansel Adams Wilderness. When I packed my backpack at home, I specifically shifted over from Esbit to Butane, just to avoid some possible hassle like that. I'll probably stick with Butane until I hear that the fire restrictions have passed.