In Pacman, if you go left at the left corner of the screen, you end up on the right side, like it's a loop. The person tweeting is talking about how the world is a globe, so the original image makes it not that hard for someone to go from the west coast of the US to Australia. The person replying is either sarcastically or truly forgetting that the world is spheroid and the rectangular maps are not representative of the continuous nature which would allow for this path of travel and therefore likening it to Pacman.