Your cat is obviously starving! Just kidding.
This trick or learned behavior by your cat shows how persistent and smart these felines can be. Cats are preoccupied almost exclusively with food. Cats by nature are predatory, they are driven to find food sources. This need is all consuming. A cat will not let something as trivial as a lid get between itself and food. The only cat proof way to keep your cat from opening a container is to put it under lock and key.
Disclaimer: As of this time cats do not know how to use keys…this may change in the future.