It's slightly different. With poker, you play with drunks because they make mistakes. With order flow, you want trades from small fish who don't have any special knowledge so you market make and not be taken advantage of, yourself.
Except that unlike in casino, in stock market a Designated Market Maker can go against the crowd and "wait it out" any negative downfall.
Lets say customers bought GME and GME shoot up.
Citadel just waited out until the movement fizzled out.
They were able to hold naked short position for prolonged period of time (basically printing fake shares) to artificially increase the float
