Citadel Securities (the market maker that buys and executes Robinhood's order flow) and Citadel (the investment group) are very different companies, and they have a ton of red tape in place to prevent risk of collusion between the two.

Considering Citadel Securities makes _significantly_ more money than Citadel would stand to lose with its short positions, the thought of the two colluding to pressure Robinhood seems a bit far fetched to me.