Grease, red meat and white flour. Couldn't get much worse than that after 31 days of fasting. He should count himself lucky that he didn't get more violently ill. Some people have gotten ill from something as inocuous as eating salads too soon. After 31 days with no fat in the system and then dumping nasty grease in his gallbladder is it any wonder that he has pains.
You gave him good advice with the SWF. I would add drinking lots of fluids to keep things moving. If he gets really sick he could try an enema to empty all that nasty stuff he ate. Even if he's not feeling real ill an enema at this point would probably be a good thing to prevent him from getting ill.
He should definitely continue on with the MC and then be very gradual in the return to regular foods or he could have a really hard time getting his digestion and eliminations back to normal not to mention possibly getting violently ill.
No doubt the small amount of food kept any ill effects to a minimum. What ya'll should be aware that the breaking procedure described in the book is for the general minimum MC of 10 days. On the longer MCs over 2 weeks one should extend the return to solids for more days, I would say for a 31 day fast he should take a good 7 to 10 days maybe even longer depending of how the individual eliminations go