There's actually an investigation, both for the cause of the death(they required a blood test for illicit substances) and for the responsability of the doctor/production because supposedly they didn't want to fly him in an heli like they said they did because they weren't sure it was worth it and heli is expensive. It is a bit weird though that it happened in the first day, I wouldn't say it's impossible that someone who has a lot of trouble sleeping/not getting proper nourishment could have a heart attack, kinda like these korean gamers, but to have one on the first day.
Also supposedly didn't have any heart condition or anything, but the guy was 25 so it's really a bit weird.
Not that the french survivor is very interesting to watch, they use a much more limited set of rules and shit so you don't have all the drama and strategy you get in the US one(no individual idol, no team remixing halfway before the merge).