Micro, Superheroes often times become politically involved in comic book environments. The X-Men are probably the most prominent in this behavior due to "mutant legislation" but other superheroes do it at times, too.
There's nothing wrong with Superman flying to Tehran to take part in a protest against a corrupt government. I haven't read the issue, but it wouldn't surprise me if he stopped some little kid from getting run over by a tank, or defused a group of Iranian soldiers from opening fire into the crowd, or something like that while he was there. Or perhaps his presence deterred any form of crowd control due to fear of retribution from this invincible force with a well known moral compass.
What's wrong here, is the US Secretary of State getting pissy at Superman for going to Tehran.
The SecState, and the US Federal Apparatus, lost "the American way."