Correct. Usually similar enough to some aftermarket hard-bag mounts, but smaller, lighter as they don't actually carry the weight of the bag; they simply keep the bag from swinging around.
I'm glad stuff like that exists, but this is why I went to hard luggage and never looked back. My soft-sided luggage didn't go into the rear wheel, but they would sag like crazy as the day went on. Nothing they came with added enough rigidity to keep them in place...a serious design oversight.