If, as it seems in the article, they are using COCO to establish ground truth, i.e. what COCO says is correct, then whatever COCO comes up with is, by definition "correct". It is, in effect, the answer, the measuring stick, the scoring card. Now what you're hinting at is that, in this instance, that's a really bad way to establish ground truth. I agree. But that doesn't change what is and how we use ground truth.

Think of it another way:

- Your job is to pass a test.

- To pass a test you must answer a question correctly.

- The answer to that question has already been written down somewhere.

To pass the test does your answer need to be true, or does it need to match what is already written down?

When we do model evaluation the answer needs to match what is already written down.