Tournaments are generally won by weight off a 5 fish limit. I have fished a few kayak tournaments that use length, but I would say since most major tournament circuits use the 5 fish limit that's what has happened here.
So to reach that limit, you would go fish a given body of water along with whoever else is in the tournament. After a set number of hours, usually 8, you meet up and have a weigh in where the one with the heaviest weight is the winner.
One thing that I want to point out is that anyone who fishes in these high level tournaments are competent fisherman. But there are many different ways to fish and each fisherman has his own expertise. You have to take in to account lots of factors when fishing in these tournament and yes one of them is luck. Yes if the best spot is obvious it is a race to that spot. However these guys are fishing very large lakes with many spots, so a lot of them have pre fished the area and found multiple spots, or maybe due to timing or whether they fish have moved and now you have to search to find them. There really is a element of science and skill to it.