Even if it is logged, there are ways this behaviour could be masked.
Say a colluding miner mines blocks including this unbroadcast transaction until they finally hit the block target with this transaction included.
Bitfinex then broadcasts the transaction to mempool. After some plausible delay (but a short enough one that no one else gets a chance to mine it), the colluding miner publishes a valid block including the transaction. No one can confirm that the miner didn't receive the transaction from mempool like everyone else, and then 'get lucky' shortly after.
I'm not saying this is what happened, I think user error is more likely. But it can neither be ruled out nor easily proven.
Say a colluding miner mines blocks including this unbroadcast transaction until they finally hit the block target with this transaction included.
Bitfinex then broadcasts the transaction to mempool. After some plausible delay (but a short enough one that no one else gets a chance to mine it), the colluding miner publishes a valid block including the transaction. No one can confirm that the miner didn't receive the transaction from mempool like everyone else, and then 'get lucky' shortly after.
I'm not saying this is what happened, I think user error is more likely. But it can neither be ruled out nor easily proven.