Quoting a 2015 manual doesn’t mean the BSA always had that policy. They certainly did not when I was a Cub Scout years ago. Back then, at a Cub Scout meeting, we threw knives into the ground at each others feet...
This policy is a surprise to me, too. However, maybe we just didn’t know it was the BSA’s “shooting sports policy.”
Just asked my oldest son. He doesn’t remember any water guns at troop meetings or anywhere with his troop.
I was a scout in the 1960's and that kind of activity would get your toten chip jerked.