If the drone had it's transponder on, the track is easily available. If it had the transponder off, it was up to no good and a threat which should not be tolerated.
This is a spy plane, trying to spy on a hostile foreign nation. Of course the plane had its transponder off and of course it was up to no good. Spy planes/drones, well spy. if it was broadcasting its location, Iran would have been tipped off they were being watched, and their radio signals possibly intercepted, and would have the opportunity to try to impose countermeasures against being spied on.
A plane flying over international waters without a transponder on is not a threat and is free to fly under international law. Shooting down a plane traveling in international airspace is an act of war; this is true if the plane had its transponder on or off.
Iran is being attacked mercilessly by aircraft flying without transponders and is under direct threat of imminent attack of their soil. Nobody even really denies that planning for an attack was the mission of this aircraft which was being operated by a belligerent as part of a military operation.
Under these conditions, and especially under sanctions which are by some legal definitions an act of war in and of themselves, I would say that Iran had every right to shoot down the aircraft even if it were in international airspace, but I doubt that it was. What the U.S. says about it's location has zero value with me since they have proven time and time again to be chronic liars, and I suspect that Iran would probably only have fired at it if it were over their airspace.
It would be totally cool with me if Iran could take down satellites too and totally drive the U.S. military back to the U.S. territory where it belongs. I'll bet that even if scum like the Zio-cuck Saudi monarchy love them some sheckles, the rest of the 99.5 percent of their nation's souls are don't and would happily bum rush the main source of grief in the Middle East and solve the problem. Egypt same. Turkey same. After they take care of certain business at the top of their own countries first of course.
Edit: I should add that I don't want to see ^^^ happen. Mainly because these 'chosen people' would swarm over to my country and start demanding reparations from me, and our political leadership would gladly give them anything they demand. And more! I'm strongly in favor of a 'homeland' for the 'Jewish people' who are into that apartheid sort of thing...and one which is as far as possible away from me. I'm just saying that I could see it working out that way.