Why is there a green bomber in Dyna Blaster multiplayer?

In Dyna Blaster, there is a multiplayer mode. Regardless of how many players are playing, the leaderboard on the top of the screen shows scores for 5 players. However, in the match setup screen, you can only set 2-4 players. Also, in the settings, you can set up controls for up to 2 keyboard and 2 joystick players. There is no fifth. Then why is there a fifth, green player on the leaderboard?