Big mistake? One drone, no human casualties.

Well, you have to put things in perspective.

Remember the Iranian passenger plane that was shot down on 3 July 1988 by an SM-2MR surface-to-air missile fired from USS Vincennes, a guided missile cruiser of the United States Navy.
The Iranian passenger plane was hit while flying over Iran's territorial waters in the Persian Gulf.

It probably was not even a mistake.

The aircraft, an Airbus A300, was destroyed, and all 290 people on board, including 66 children, were killed.