In this photo it looks like Barton is asking if Johnson is OK, after the bigger boys stole his Transformers lunch box. Just before this Barton had actually put his forehead into Johnson's face. I have watched a video of the incident on 101greatgoals.com and it looks as if he did that "squaring up" nonsense that chavs do in your local night club do when they have had too many vodka redbulls, "lookin at ma blonde?", as they say in the North-East of Scotland.
The red card was pretty soft but rules are rules. That is not good enough for Barton or Neil Warnock who are convinced Johnson conned the assistant who gave the decision. Warnock spouted his usual paranoid everyone hates us, they are cheats bull shit. From Barton's notorious twitter -
Well feel for the officials, they've been conned. Admitted to me at HT they never saw it. I was pulled back 1st, then kicked 2nd!I iz well feelin dat Joey. It doesn't actually matter if the referee sees the prior incident or not, you are not allowed to headbutt people. Then again this is a man who stubbed out a cigar on a youth player's eyeball, assaulted a fifteen year old Everton fan in Thailand, punched a man outside McDonald's (who was already on the ground) fifteen times and then used his dragon punch to break the teeth of a sixteen year old minutes later. He does like the Smiths though so I guess he's not all bad.