I am pretty much this was because of fat fingers, but how an earth there's no security measures for this kind of thing? It's 2020 already and after seeing this kind of mistakes, i am pretty sure that ETH adoption is further away. Just one warning message informing about the possible huge mistake could have saved millions for this guy.
I never thought that this thing happens, sending $2,6 million as gas fee. If i lost that amount of money i would been so depress. I could even buy my own house and car with that amount of money.