It might be a honest mistake maybe the user in question was in a hurry and didn't confirm all inputs to the transactions. For all we know, both cases might have been a mistake because I doubt the possibility of someone paying that much when the value being sent out is around 3/100 of the gas fee? It can happen to anybody this is why it's a recommended practice to strictly verify all inputs before a transactions is sent out and broadcasted to a network.
Edit: Paxos have confirmed that they did the transaction and that it was a mistake:
https://finance.yahoo.com/news/crypto-miners-debate-500k-bitcoin-063851495.htmlAlthough they didn't disclose how it happened, my best guess is that they made the transaction programmatically rather than a manual input.