Actually the response to this Op case is still a hot topic of conversation because everyone has different opinions and thoughts, like now you think it's gambling because there are several risk triggers to gamble using real money.
For myself, betting for free to get real prizes from the results of this prediction can be considered open gambling as long as we consider this only a game that allows us to earn money from this guessing or prediction game.
But it will be gambling if the person is triggered by this prediction and bets using personal money to predict, then this is gambling.
So all responses return to their respective mindsets.
But there is already a written rule about what to consider a gambling or not. So personal opinion does not matter on this since a fact is already written about what is considered to be a gambling. It is actually a known topic but many of us here thinks that they know better than the set of rules stated and established by the dictionary and legal documents about gambling. It is written in all definition of gambling that it
needs a stake, money or something of value to be put to risk in order to get a reward. How can someone consider a game that has no stake in hand. Without stake there is no risk, without risk it cannot be considered a gambling even though there is a prize ahead. It can be called a game of chance if prediction is involved and there is no need for the player to stake money.