OK. You're right.
All that being said, and given his latter rather than former remarks, and given his body weight, and given the length of his sessions, and given that it's not described as the sharp pain of a cramp, but, rather, as grumbling, and I'd say the little guy (5'10", 143#, according to his profile) just needs to eat some more.
Sometimes, the most obvious solution is the right one. In fact, it most often is.
Even if he has cramps, that's usually a symptom of not eating the right foods (electrolytes), and almost always indicative of low sodium (not potassium). In either event, cramps, or hunger pains, nutrition is almost certainly the right answer. Low calcium can also cause cramps, but, it's almost always an issue of low sodium in hard training athletes (hence, salt pills, and sodium in Gatorade, etc.)
It gets down to proper nutrition, in either event.
I've taken time to research this for the poster, and here's a link with some good information, that he should be able to read on his own, all getting back to proper nutrition.http://en.wikipedia.org/wiki/Muscle_cramp
Quoting, he says, "I get grumbling and pain from my actual stomach, not my ab muscles themselves." (Note that he edited the original posting.)
Ab cramps will bend you over in great pain. If you get them, you'll know. This sounds like he's just not eating properly, and given all his descriptions, and his profile, I'd say it's a qualified guess.
I've had hunger pains, too, and it sounds exactly like hunger pains to me, and with someone so thin, I think it's very much more probable.
I'd ask that the poster consider the advice is offered objectively, and from 33 years of experience in the weight room, and that the poster accept, or reject, the advice in a mature manner.