Perhaps the downing was executed prematurely, before the aircraft had travelled far enough to be able to blame the shoot-down on the US.
Definitely a possibility. Alternatively, those were Russian made rockets. If it’s like Syria, there are thousands of dual citizen Russians living in Iran. Weather is nice. A little vodka, being upset when you realize Iran is standing down....accidents like this seem to happen a lot in that part of the world, unfortunately.
It is normal for SAM installations to track all aircraft. It is just part of training. I suspect an idiot launched a missile in error. If not in error I am puzzled by this action.
Very interesting theory.