It's Choose Your Own Justification Time!Take a close look at the checker-board in the penultimate frame, and then choose the following reason why it does not bother you enough to email the author.
A) You don't know how to play checkers, and are okay with that since you are relatively sure you DO know how to play the firing mechanism of an AR-15, and are more interested in focusing on survival skills in today's modern world.
B) Obviously when force-mapping a five-dimensional probability curve onto a two dimensional grid, and then further forcing that into a checkers match, a few rules may safely be bent.
C) In the 31st century, "checkers" will have evolved to use more than just one color of squares on the board. The board will have evolved, too, so that the game can be played with sticks, dice, and an AR-15 if the players are up to it.
D) You wish to engage in an apathy contest with the author. If he doesn't care enough to fix this discrepancy with the checkers people know and love, you don't care enough to email him.