There's no reason to believe that the incidents so far have been anything other than random nutters. The attacks have been amateurish and ill conceived and it is highly unlikely anyone but the nutters themselves are behind them.
Vilks is an artist with a wish to provoke and create headlines. It is his living after all, and he isn't a very good artist so he needs to provoke.
Naturally, it is his right to do so as freedom of speech still applies. Attracting the attention of random nutters means the rest of us have to use our resources to protect him from those people who would take offence. I just wish the resources were as forth coming when the victim of credible threats are women's shelter employees, human rights lawyers or just some young woman who has had some success with a non-controversial blog.
Setting aside the fact that violence never is an appropriate way of protesting someone exercising their right to free speech, which I hope we can all agree on, there is very little merit in Vilks' stuff. It reminds me a lot of the type of cartoon you would find about jews during the Weimar years. It is actually more or less exactly like it.
The film he was showing in Uppsala was not his, but the work of an Iranian artist. As I haven't seen it I don't have an opinion on it. But it is likely he could have shown Barbapapa and still get head butted at that point. The person who attacked him was clearly there to protest Vilks no matter what was being shown.
Also, as evidence from the constable who helped protect him and remove him from the scene says that what he perceived as a headbutt in his chest was likely inflicted by the police grabbing him to get him out of the way. No violence had time to happen so we can't know if the person was about to get physical or just scream in his face. Likely? Sure. Certain? No.
The arson attempts smack of kids, or possibly Inspector Clueseau.
The only thing that seems to get a rise out of a jaded public these days is the prophet and peedos - and Vilks probably wouldn't be comfortable condoning the latter.