It's possible to set this up in a way that gives them plausible deniability (by broadcasting the transaction publicly after the colluding miner confirmed it has

It's possible to set this up in a way that gives them plausible deniability (by broadcasting the transaction publicly after the colluding miner confirmed it has a block), so this could have been a way to repay debts with funds that aren't legally/technically allowed to be used in this way. I do doubt that explanation though, as $23 millions is nothing for Bitfinex and any of their execs could get this amount from personal funds if it was really needed.