I think you're severely underestimating how stupid some people can be without malicious intent. Not that I'm justifying their behavior in any way, but it's possible they're just really stupid.
Not for nothing, but it could also be tourists. Not defending nazis, because I would argue that being drunk lowers inhibitions, but it doesn't make you a nazi.
Yes, tourists sometimes think it would be funny. But this did not happen at the Oktoberfest in Munich. It was an Oktoberfest in a village in Saxony with about 2500 inhabitants (actually a collection of several villages). I would bet the chances of tourists being present are very close to zero.
Right, but we're talking about the people in this photo. Germans and Austrians know not to make nazi salutes because you could face legal repercussions. That's a weird concept for Americans, though. I kind of wish we did jail more nazis, but that's besides the point.
And I think you are underestimating how much of a deeply ingrained taboo the nazi salute is for the typical German. You are right, some people can be very stupid, especially drunk. But no German who has not been in some way socilized among nazis would be stupid enough to ever casually do a nazi salute. You just don't do it.
The only exception I might allow besides actual nazis are very stupid or drunk (or both) teenagers trying too hard to be edgy. And even then most people would find it hard to believe that they're not at least right leaning.