Love how Welker ducks and its somehow Swearingers fault, according to some. Unless they switch to two hand touch, this type of stuff is going to happen.
Also, almost guarantee the concussion is from how hard he hit the ground, not hitting Swearingers shoulder.
I think it's a clean hit, but those penalties seem to be called based on how vicious it looked rather than point of contact and relative body position.
In my opinion, you can't say the head was targeted on a receiver who was going to the ground just prior to the hit, and you can't say it was a defenseless receiver when the move toward the ground is a defensive one. If he was truly defenseless, the shoulder contact would have been made with the chest.
But that's just the league now. The term "defenseless" is basically meaningless because of how far it has been expanded. I remember a Raider got flagged in Minnesota a couple years ago for hitting a defenseless receiver who had caught the ball and took a step up field. It's superfluous language at this point.