Yes, if was dehydrated and drank the wrong thing for it, that could trigger a seizure. Sports/energy drinks are not safe for everybody. If one of his hip friends gave him a sports drink, that could have made him crash.
I remember basic training in south Texas in the middle of August. That was real hot and humid. Guys were falling out often. 4-5 days in a nice hospital with IVs and various tests. That time still had to be made up to complete the course. We all graduated by running 1.5 miles in less than 14 minutes in worse conditions than when we fell out.
It was typically a blood chemistry imbalance for the conditions. We eat different things when it's hot or cold.