I’m not a friend of the criminals in charge of Iran, and I will be glad when all of them are with their 72 virgin camels in hell not heaven.
However, Iran is a sworn enemy of ISIS and probably a few more very radical ISIS like groups.
Before the ISIS took over of a lot of Iraq, a large % of the mid east air traffic flew over Iraq. Now that traffic flies over Iran as shown by the link below. It will take 30 seconds to a minute to upload the planes in the radar:
http://www.flightradar24.com/33.33,44.28/6
Then, throw in the missing/seized airplanes now controlled by ISIS like groups, and Iran is probably scared they could be a target of terrorist flown airplanes:
Report: Nearly a Dozen Commercial Airliners Missing Ahead of 9/11 Anniversary After Islamists Overrun Libyan Airport
Iran is going to be very cautious about any plane not following an up to date flight plan.
We don’t know who owns this charter plane and it’s country of origin. It probably will not be a US plane as our insurance companies are not covering planes flying over Iraq and Iran.
I tend to agree with your assessment. Iranian regime doesn’t want a confrontation with the US now; this isn’t 1979, especially given IS is actually in Iran’s backyard. They’re definitely very concerned about IS. Al-Baghdadi in fact threatened the iranian regime as far back as 2007 & meant it too.