I'm sometimes guilty of commenting without thoroughly reading the linked articles but in this case a simple glance at the photo in the article would've answered your question.

I mean, if he's not, he's picking a weird flag to pose in front of.

Dude had a Hitler mustache, wearing a white pride t-shirt, and is standing next to a Nazi Swastika flag in the pic. That's pretty telling.

A critical point being "... and it was clearly not in jest" because Mel Brooks would be capable of being miscast, in this reading.

There is the concept of the "self-hating jew" which is a bit of a "thing" and it's often thrown by proponents of the state of Israel, and any Jew which questions the legitimacy of actions of the state in current times.

https://en.wikipedia.org/wiki/Self-hating_Jew

I'm not sure it's "clearly" sincere in this case, since he also had a persona as "a rock climber known to others in the area as a politically progressive vegan named Jesse James." Though I don't see any reason to give him the benefit of the doubt here either.