Predicting the price of a highly volatile asset like Bitcoin is a very complicated task. If you are lucky and get a week when Bitcoin will not have many variations, it will be easier to guess, but more people will make very close guesses, making it difficult for the manager to determine the winners. That is why the prize is so high.
Guessing the probability of a rise, fall or reversal is one thing, trying to guess the exact price of Bitcoin is another, so I prefer to think that it is really a matter of luck.