They are obviously not professional enough. Either the MB team, or the range supervisors, or anyone else in that chain.

If your range is situated so close to populated areas that you can fire a projectile from a makeshift cannon out of the bounds of the range, then get a bigger range. Or a smaller gun. I have no idea how big their range is. However, it was apparently not big enough.

I don't know if the ball hit the hill or the sky or a bird on the way or anything else that might have happened. I weren't there. I also obviously understand that they didn't plan for the ball to go though those houses. However intentions does not change facts. Neither do regulations nor safety procedures, nor requirements.

If you cause an accident then you havent gone to the utmost of efforts in preventing it. The utmost of efforts might also include not doing it at all.