[hanasu]

To put it extremely simply, there are specific ranges of acceptable statistics about what winning play looks like in poker. With thousands of hands of data winning players can intuitively pick out stats that are out of line.

For example, there are two related stats: went to showdown, and won money at showdown. These calculate how often you get to the last card and reveal your hand against another player/group of players to win the pot, as well as the frequency you actually win these showdowns. Generally, the more you are showing down hands against opponents, the lower your chances of winning money, simply because it's not always possible on average to have better hands than your opponents above a certain frequency of times you're getting to showdown. If a bot/player had access to other players' hole cards (like actually happened on the Ultimate Bet network) a telling example might be that they go to showdown way more than average while also winning money at showdown far above an average rate.

There are tens (if not hundreds by now) of common poker stats, this is just a simplified look at one related pair.