Ignorant people who do not understand the basic precepts of elementary, common-sense physics do not know that, when an unsupported cartridge goes off, it is the case which moves off at a rapid rate, while the heavier bullet stays still.
The foolish child pointed the .22 cartridge away from himself, expecting that the case would remain in place while the bullet would depart.
Of course, the exact opposite happened, which is why the flying case removed his eye.