Do you normally go on conspiracy theories first?
Your #1 is wrong. A lot of Norwegians typef better English and more natively than most Americans can.
All the rest of your stuff depends on your #1 which is blatantly wrong.
His other writing on the web was very broken English, the Facebook comments were very casual English. I'm not thinking conspiracy theories but pranksters putting up these pages like they do every time something like this happens and a media who never does due diligence falling for it. Everything else adds to the suspect, the biggest to me is how quickly posts were added to the wall. Music videos being posted within seconds of each other, a couple dozen within a few hours time with nothing else at all. There was one where he posted the video, made a comment, then posted another video within 10 seconds of the first. It screams someone trying to fill up a profile quickly.
1) Um, begging your pardon, but it is a logical impossibility for non-native users of English to speak or write "more natively" than actual Americans, because actual Americans define what "native" is, warts and all. You've posited an absurdity.
2) Furthermore, the remaining evidences do not appear to me to be dependent on the authenticity of the English used. They are independent lines of inquiry.
3) As for “conspiracy theories,” dumping all concerns aside by hastily applying the pejorative “conspiracy theory” label is nothing more than a way to prevent a dispassionate consideration of all the rational possibilities. And in a time of great political conflict such as this, it is irrational to ignore the possibility of deception calculated to harm the public image of key players in the struggle. It sets one up for serious harm later. Like Kissinger said, even paranoids can have real enemies.