Actually having four limbs on the ground, or, indeed, having four limbs in total, is not a requirement here. Duh.
"all" fours. I don't see how that's difficult to understand. You can certainly have something with four limbs and if they're on all of them then it's on "all fours" but if it has 6, or 8 or 20.. and if 4 of them are in contact with the ground it's not "ALL fours".