> Citadel just lent someone money to close short positions worth a very significant percentage of their total assets?

Yes. Those other assets are presumably uncorrelated to this short position. If they were fire sold, depending on the assets, they could have gotten 20¢ or 30¢ on the dollar.

That discount gives Melvin the incentive to borrow, even at exorbitant rates. It protects the rest of the portfolio. With the bailout, the GameStop loss is capped and eaten by LPs. That sucks. But it sucks less than eating that loss and selling off the rest of the portfolio for peanuts.

> Melvin did not close their shorts(as they said they did)

You're alleging securities fraud. This may be the case! But we have zero evidence of it. And if Citadel and Point72 invested $3bn to aid and abet securities fraud, that would be quite stupid.