Is a stomach bug the only thing (besides food poisoning) that could cause fever, vomiting and stomach pain in a 10 year old?

Food poisoning is a toxin based process and seldom causes significant if any fever. Fever, stomach pain and vomiting in a kid is usually one of dozens of gut viruses.

Agree with Dr Ferguson. Other causes can be bacterial infections like Salmonella bacteremia or typhoid, protozoal invasive disease like amebiasis or giardiasis, heavy parasitic infestations. I hope child is better by now and he has none of the above. .