The reason was to make shooters aware of the lethal range of such a common bullet. Uniformed people raced forward to laugh off this claim. There are many software programs on the market that attempt to tell us how far a bullet will travel. It is obvious those programs which failed to note this type of danger can and do not take into consideration such factors as terrain, wind, humidity, and just plain bad luck from whatever influences there are on a bullet. It is obvious we still do not have a total and complete understanding of ballistics at long range.
Bullets do strange things.
This case took place in a very rural area. The odds that this stray slug hit the youth are beyond measure, but it did happen. In an urban setting the odds would increase many times over. Play it safe. We will try to put up the actual reports for the doubters on the web.