There are a lot of things that don't add up here.
1. How could Iran's air defense tell the difference between an unmanned drone and manned spy plane in Persian Gulf but not be able to recognize a passenger plane?
2. This plane was only a few minutes away from the airport and was flying away from it so even a simple radar and operator should've been able to recognize that it's moving away and unlikely to be a danger. If it was flying from abroad towards Tehran then it would be more understandable.
3. How is it that every foreign intel, even Canada's intel, knew about a missile having been fired by Iran's air defense system but Iranian defense department itself didn't know and didn't have inventory of missiles fired until two days later?!!
4. What is the explanation of the video capturing the moment of impact? Are we to believe that some guy in Iran in the middle of nowhere with dogs barking in the background just so happened to have his cellphone camera on at that exact part of the sky and just accidentally captured the moment of impact and then had the knowhow on how to send it to New York Times or whichever news outlet got a hold of it first? And you can hear the dog barking in the background but no word from the person shooting the video to at least comment about what he saw in the sky!
5. IR's explanation is that the plane made. a sudden turn which raised alarm and caused the "person" accidentally think the plane was a threat. But the plane didn't make a sudden turn until after it was hit. It only made the sudden turn because it wanted to turn back to the airport for emergency landing! WTF.
I would not be surprised if some rouge elements in the defense department orchestrated this and the IR defense department is now too embarrassed to admit that it may have molls in such sensitive positions and would rather just say it was an unintentional mistake.