I noticed an interesting stat today. LA's best face-off man in this series hasn't been Kopitar, even though he's won 57% of his draws. It's been Nate Thompson, winning 24 out of 30 draws, for an astounding 80%. It's too bad that he's not very useful in any other way or else that proficiency could be better taken advantage of. At least he's proving useful, which is more than can be said for just about everyone else in the Kings' bottom six.
He didn't blow the coverage, that's the Kings standard breakout on a faceoff win. Rieder just got beat by Smith to the loose puck and Muzzin chased a puck he was never going to win instead of staying with Karlsson. Doughty did absolutely nothing wrong on that play.
You made this point last night and I kept thinking about it afterward and today, so I decided to look into it by reviewing as many defensive face-offs that I could find in this series. What I noticed is that, more often than not, when the Kings win the face-off, both defensemen drop back to or below the goal line. Where Doughty went is where the inside defenseman seems to be coached to go to receive the puck. The problem is that he never received the puck because Reilly Smith got to it first.
You can blame Rieder, but I'm not sure that there was a whole lot that Rieder could've done to prevent Smith from getting to the puck without getting an interference penalty for it. Muzzin was the closest player to where the puck was drawn back to, yet was beaten to it by Smith and Rieder, who were both further away. That was his puck to retrieve (and either clear it along the boards on his side or pass to the open Doughty) and he was too slow to get to it. He's a slow-reacting defenseman to begin with, but it also didn't help that he and his linemates were already tired because he had just iced the puck to create that defensive zone face-off.
For those reasons, I blame mostly Muzzin for that goal. Doughty could've reacted to the missed coverage better, and he definitely looks like a goat on the surface, but I think that you're right that he wasn't out of position as far as the system goes.