The minimum miner fee that is required for a transaction to be processed promptly is therefore constantly an open question / constantly changing, which gives rise to services like https://ethgasstation.info/ which attempt to tell you how much you should reasonably expect to pay.

In terms of how today's outcome is possible: when you are submitting a transaction, any amount of ETH that you have on your account could validly be spent as the fee.

So in this case, either by human error or a software bug, someone with a large amount of ETH in their balance essentially spent all of it on the transaction fee.

The miner _gets_ all of those ETH. So some lucky miner just got a huge spike in profit.

Previous situations like this have been the result of the transaction author (or their software) making a mistake.