If the truck was hijacked, then I wouldn't be surprised if this turns out to be a spur of the moment thing due to our stupid actions last night.
Because everything in Europe was totally chill before that, and Sweden = literally Donald Trump despite not even being a NATO member?
It seems pretty spur of the moment to me. He'd have done it sooner or later, yes. But there is a reason why they are and have been killing us for years, and it is a hell of a lot more complicated than a few controversial passages of the Koran. They view us as occupiers. What we did last night did nothing to stabilize Syria and everything to only further inflame anti-American sentiment.
I mean, whatever your opinion on the military action this seems wrong. I don't see why Salafis would be particularly irritated at a strike aimed entirely at the leadership of the Syrian regime.
The action of the US launching another attack in the Middle East itself plays to that image, regardless of who it was directed at or why.