Oh wow, what a costly mistake.

The question is, how can something like this happen?
At some wallets it gives you a warning if the fee you chose is way higher than necessary but 19btc, come on. Any wallet should stop the person of making this transaction as it is an obvious mistake.
Maybe now, after this story got public, wallets will make some adjustments to prevent something like that.

That's really some insane stuff. Hopefully the person has like 1000s of btc and can live with the error. This type of mistake can break a person and ruin his/her life forever otherwise.