I believe the normal term is "gaming a benchmark test".
Nothing in what you quoted is related to that. It's a normal way to train and test a classifier.
The only way to determine if it's brittle is to test on a different dataset and look at the sensitivity and specificity.
Even so, there is nothing wrong with a model that is trained to a narrow domain when it doesn't need to deal with "wild" images.
That's just good developer practice, not "benchmaxxing".
Benchmaxxing is when someone presents a model as being generally smart, but actually quietly overtrained it on some benchmarks that were supposed to be proxies for general information.
If you train a small model on a specific task that's not "benchmaxxing" because there's no deception involved. It's just training a model for a task.
So it is not solving a task, it is solving the same test set. You can easily see these in simple OCR datasets like mnist. Draw a number yourself. It would be much less accurate than the 99% that good architecture claims.
The 200 test images here are 'wild'. Fine-tuning in-domain is the whole point. This is what model training is. A skin cancer diagnosis tool doesn't also need to generalise to dog breeds to be valid, and will almost always perform worse if it does.
I developed many models from scratch deployed in various fields.
When you want to automatically detect a pathology from a give scan, you want it to be model that you own, train, use, and update, and not a generic vision capable LLM.
This is NOT what benchmaxxing is. You want the model to be accurate in terms of your cared metric- depending on the problem.