Is this a Danish idiom?
Nah, it's just as strange in Danish as it is in English.
no wonder that the hungry dude is found without food...
Could "på bakken" mean "on the ground" (as in norwegian)?
"på bakken" means "on the hill" as far as I know
OK, tak nordfra. :)
Bakken can also mean the tray (as used for food). Will of course result in an equally meaningless sentence :)
uden should also be translated to "with no", as in found on the hill with no food.