It's not a false flag (we really gotta stop doing this, people), the guy literally supported the AfD, if anything they were probably pretty nervous that this would fuck up their chances when they're so high in the polls.
The AfD lucked out that for one the media was super irresponsible for jumping on the "he's an islamist" angle when the guy was literally a saudi atheist, and above that is that the fact that he's an arab immigrant, and that probably matters to anti-immigrant germans MORE than the fact the he was a, I assume, pretty well integrated atheist AfD supported.