Either they have grossly incompetent idiots in their control rooms or they meant to shoot it down for some other reason.
I have to admit to a certain curiosity. As civilians we don’t really get to see exactly how these missile systems work.
Are they completely self guided and unstoppable once launched or was there an abort option that could have been transmitted?
I believe it was two missiles on the video. Probably set to the wrong automatic fire mode or something along those lines.
The question you pose would be sensible only if the Iranians hadn't double-tapped the commercial airliner.
Regards,