I'm not suggesting that this specific transaction was actually washing bitcoin but I got me thinking this might be a way to do it because large pools have so much hash they can afford to work on out of band transactions.

I don't know about this specific transaction but a pool could be paid out of band to mine a transaction with a large fee then pay a portion of the fee back to the sender and get paid for the service. A PPS pool like antpool is well setup to do something like this because the miners only get paid out of the block reward not the fees.