Hmm... it sounds like someone had a disagreement (aka 'nice argument') with someone who feels that this 'cake mix' cook is a superb chef.
I think someone could be an excellent 'box off the shelf' cook and be considered someone who had decent cooking skills. Are they considered a 'great cook?' Well, it depends on the food, in my opinion. I take lots of boxed foods and add things to them to make them much better. Does it take away kudos for the fact that I'm using a pacakaged product? Not really, but does limit the cook and I would never call that person a chef, per say. Canned vegetables shouldn't even exist, so maybe that point alone disregards this person as a cook.
Some people never even get to the cake mix, or the fried frozen chicken. So, I'd say this person is on a good roll, but to move beyond the pre-mixed batters and the microwavable side-dishes. Are they a great cook, probably not if they are *unable* to do things from scratch.