M.P.
Carregeenan is a natural product made from sea weed. It's used to thicken things in much the same way as gelatin. It's not harmful. He has no better chance of getting food poisoning from carregeenan than from gelatin.
The main symptoms of food poisoning is vomiting and diarrhea. It's highly unlikely that he would get seriously sick. He'd vomit up the stuff within a couple of hours and then he'd be fine in a couple more hours.
I've had food poisoning a few times in my 70 years. I've gotten sick within a couple of hours. Vomited and pooped. Went to sleep. Woke up the next morning feeling just fine.