I'm wondering if this is money laundering.
Alice has dirty bitcoins that can link him to illegal activity.
Bob is a miner.
Bob keeps adding the TX to the blocks he is trying to solve. As soon as he solves the block, he notifies Alice so the TX goes to the network and Bob releases the block.
It looks like Bob got the TX from the network. But the dirty coins are destroyed.
Bob then sends Alice the equivalent value (less a fee) using existing coins or using the coins from the block reward to several addresses controlled by Alice.
Now both Alice and Bob are cleared of any scrutiny and the laundering is complete.
this case was most probably a mistake in the code they were using which sent big fees.
but your theory is interesting but it doesn't sound right. because if you want to launder money you will try to cover your tracks
in this case when Alice sends her dirty bitcoins to Bob and includes a big fee, it is so obvious what they are doing besides doing it a couple of times to a miner called Bob will put Bob in law enforcement watchlist and following the coins going into his blocks and out of his known addresses will lead them to Alice too.
Alice doesn't have to send them to bob.
Alice can create a transaction send a small amount to a random address neither care about and just include a large TX fee.
Bob just includes the transaction in every block Bob attempts to mine and Alice doesn't send the TX to the network until Bob has found a block.
There's a small risk another miner will find a block at the same time, but really all bob needs is a way to communicate with Alice that Bob solved the block to trigger Alice to send the TX out to the network at the same time Bob releases his block to the network.
Then it looks like Bob got the TX from the network if forensics is done because Alice has sent the TX out to the network.
There's no way to prove any collusion between Alice and Bob through the blockchain and the dirty coins are replaced with fresh coins.