AMount of contact doesn't matter, I really don't get the lack of logic. In terms of the red card, he reached out to a player and reached really stupidly far just to catch him in the face, amount of contact doesn't matter, intent does, he threw his arm/hand out at the guy.
On the guy, it's instinctive in every situation that if you have contact made on you your immediate reaction is to back away from it. Not only that, getting a finger or even worse a finger nail in your eye can damn well hurt.
How the player reacted is irrelevant because the red card comes from his action. But when someone catches you in the face a NATURAL reaction is to back away from it and if you happen to be running that will often mean going down as you try and pull away from whatever contact it is.
Also, Townsend says it's not a red, thus, certainly a red.