"Here is a challenge, designed to be unsolvable or so. We'll give you a bazillion dollars if you complete the challenge, and, in the meantime, we will use your attempts to train an as AI that will be worth the cost!!"
But the people involved in this haven't signaled that they are in that path, either in the message about the challenge (precisely the opposite) or seemingly in their careers so far
So I guess I don't share the concern but a better way to phrase your comment could be -
"how can we be sure the human-provided solutions won't turn out to be just fodder for training a RL model or something that will later be monetized, closed and proprietary? Do the challenge organizers provide any guarantees on that?"
Human: "They're quite challenging, this might be a trick to engage activity for the purpose of training models."
skrebbel: "You're stupid".