Is it unprecedented for an F-16 to get hit by its own bullet(s)?
I can find no record of an F-16 shooting itself down prior to the Dutch incident. There is certainly nothing on the wikipedia page for aircraft shootdowns or anywhere else I can find.

However its not the first aircraft to manage the feat. In 1956 a US Navy F-11 Tiger became the first aircraft to shoot itself down, whilst testing its cannons on a test flight. The pilot fired a long burst of cannon fire then entered a shallow dive and hit the afterburner, shortly after the aircraft was hit by its own bullets.