A party who is posting bond must deposit the bond amount. A surety that is posting bond can retain the funds because the court believes (for various reasons, in most cases some kind of licensure and disclosures) that they're good for it and they will lose their ability to conduct that business if they're lying. He's agreeing to give the cash to Knight so Knight can make good on the promise of paying if he loses. If he didn't give it to Knight, it would have to go to the clerk. Nobody is getting paid immediately under this arrangement.
I'm not going to second-guess the AG's office here, but you are correct that this is a very weird arrangement, since Trump gets the bond back if he wins. But I don't think they're convinced they'll win and they're writing that money off. I still think this makes more sense as a way to Knight to increase Trump's existing indebtedness (and their secured positions) to Knight. Trump gets the win of not handing any money over, Knight gets a bigger piece of the pie when it all collapses.
Edit: There's a lot of ink spilled about Trump getting various special treatments from the various NY courts, most of which is people venting frustrating that he isn't being tarred and feathered. This, I think, is the first good example of special treatment. Nothing about this bond makes any sense, the company is not trustworthy, and they're still relying on that untrustworthy company (not even a bondsman) and the even less trustworthy Trump to more or less be good for it. The whole thing is completely bizarre and reeks of the AG and the courts not wanting to poke a bear or look like they're being mean to Trump.
