Another Lurker Delurks
I have to assume that all three tribes felt they had a chance at winning fire either in a challenge or get it in TC. Since they mentioned working on it for "several hours a day" if they really thought they needed to start fire to survive I would expect them to work on it quite a bit more. Especially the first day or two when they should have energy.
The rule of 3's ie surviving for only three days without water would indicate that they are drinking water from someplace. They stated that the survivors were given canteens, did the canteens have water in them?
It looks likesome at least did "study" how to make fire, but not necessarily practice it on a tropical beach setting.