You may call it a contest where those who predict correctly wins the prizes. The difference between this and gambling is that here you are just participating in prediction without investing your own money while in gambling you would invest your own money in order to participate in prediction.
Anyways I do agree that most people will consider these two scenarios as same and will treat both of them as gambling.
people don't understand the context here, can gambling without money be called gambling, it doesn't mean that participating in a contest can be called gambling even though playing gambling or competition because without using money it's hard to say it's gambling because there's nothing at stake, even in my opinion it's gambling using fake money or demo game can also be called gambling but unfortunately it is only fake money as a demo.
We cannot consider any betting without money as gambling. There are some situations where money is not exchanged but is treated as a bet. I have some friends who sometimes bet with some others friends where they don't prioritize money. But if they lose the bet they are obliged to give treats. Can i consider such bets as gambling? Definitely not, Because there is no direct relation to money. Moreover, no one has any regrets even if they lose.
That kind of play is different in gambling bets as this certainly talks about money and should be placed upon betting. Gambling is money, apart from that can't be considered gambling anymore as the loser will oblige to pay for his lost bets from his pocket and there is a sort of feelings or emotions. And to that example that you've cited, despite the fact that you lose, you are still happy doing it, treating your friends, unlike the feeling that you lose from gambling - that was a disappointment.
That's what we called friendly gambling or friendly game because there is still pride involved with it. Even without money, you can still gamble as long as there is something on the line, even if it is just a simple command, like if you lose, you'll do this. The feeling with it is not also the same with money on the line because this is more fun as both of you will be doing it and friendly mocking each other. Though this still depends on others views, we are not the same.