If that were in fact true that it was in international waters, why was Iran the one to collect the debris instead of us? If it fell in international waters you can be sure we would have made every effort to collect it to keep the Iranians from inspecting our technology and possibly reverse engineering it.
Since our guys were gearing up for a counter strike, I think sitting vulnerable dead in the water to collect debris just outside 12 miles of Iran with Iranian gun boats probably looking for confrontation about, would not be the first priority. Second, finding some fragments drifting on the surface after the event wouldn’t be difficult, and they can drift into their waters by currents, or they could all be faked anyway. Having done lots of FONOPS in my earlier navy days, I am going to believe the Navy when it says the drone was legally in international airspace.