It will depends on your action to differentiate if this is an investment or challenge
Basically if you are not putting your stake of 0.1 BTC into this and/or take a cut on the profit after this game reached it milestone than this will be consider as an investment. However if you are putting in your stake and dont take a cut for the profit gained then this is a challenge instead
Basically this "challenge" is not necessary at all. By creating a stake pool and wager with it , it will be the same as wagering by yourself with your own BTC (plus you can use Joca's free tip to help you in this ) because in the end you will need to split the profit gained from the stakepool depending on how big your stake is