That would go under someone who thinks they have more information than they think they do. Perhaps you are great at mathematics and think you can estimate much better than the average bidder. The person who filled the jar is going to have even better information than you do. Or perhaps not. Maybe they miscounted or their manager added a handful before they screwed the top of the jar on.

If the market that is taking the bet also filled the jar, then sure it’s just outright fraud at that point. But the market exists to get the real information into the open. Betting that an insider just isn’t going to play is a variable you consider when placing your bet imo.

A "market" is hypothesized to be "efficient" at price discovery.

An efficient "prediction market" would more quickly resolve to its expected outcome due to not only skin-in-the-game bets by experts, but also the influence of insiders.

Furthermore, bets are likely to shape outcomes. Betting someone will be assassinated (not allowed on Polymarket) would likely increase the probability of that outcome had there been no bet at all.

the guy who put the jellybeans in the jar can put the best bet on the result, no?