I'd like to know more about this. If there was absolutely no one behind the drone area fine. If there was however, yes very dangerous and foolish and I'm sorry someone lost their expensive equipment. I don't know what regulations are on the books with regards to drones flying over a crowd of people but if this person kept flying over and around the crowd and was uninvited(private event or invite only to any media) and as long as no one was anywhere behind the direction of the spear being thrown then I'm okay with that too.
More and more we hear stories of drone tech being used unethically. I personally don't want drones being in the sky on a regular bases. As a novelty and hobby yes but not Amazon deliveries and out of control, overpopulated robot skies.