I was preparing to battle and was feeding my pet Endever pancakes, when i noticed it said Feed Endever (This has been eaten before!) Is there any significance to this? achievements for feeding pets or is it like collecting the food? Just wondering.

it's a warning for people who are going for the gourmand achievement! it means your pet has already eaten that item before ^-^ if you are just feeding the pet for battle, i'd say to ignore it

gourmand achievement, im assuming that's for pets eating different foods?

: Yes, it's an achievement for feeding your pets unique food items.

If you don't care about that achievement then you don't have to worry about it. You can even put your pet into the resort so that you don't have to manually feed your pet :)

Oh thanks! I want to get as many as i can! I was just surprised to see it!