It's 100% an error. The way you can tell is that the ball connects with his fist. Not his hand, his fist. If you connect with an open palm you can try to direct the ball in a different direction. With the fist, the ball goes anywhere.Not with the power behind it. He only just gets his hands in position and cant get his body behind them to reinforce himself. It wasn't impossible to save but it's not fair to say you'd save it 9/10 times. That can't be labelled as an error like the Mount goal.
It's not a clanger, like letting the ball sneak under you or dropping it into your own net, but it is an error of technique.