I can't verify the solution posted. It looks like it's telling you to edit the configurations of Retroarch. If your emulators are working correctly, then that solution won't help you. Can you post the attract.cfg file?
To find it exit attract mode to the command line
type:
sudo pico /home/pi/.attract/attract.cfg
Mine looks like this (some irrelevant stuff removed for clarity):
input_map
back Escape
up Up
up Joy0 Up
down Down
down Joy0 Down
left Left
left Joy0 Left
right Right
right Joy0 Right
select Return
select LControl
select Joy0 Button1
You should have an entry for down (keyboard down) and down (joystick down)