It’s a bit hard to tell from the photo (not your fault really; it’s hard to get a clear picture of these things without seeing it in person!), but it does look like early stage sore hock. Reddening and swelling is the sign of irritation, taking it to the realm of sore hock, as opposed to callous. Notably, rex’s are prone to sore hocks, so I wouldn’t be too hard on yourself re: them forming.
I would check them each day to ensure it doesn’t get worse. If you notice the skin opens/breaks, I recommend going to the vet to get some treatment, as you don’t want that to be a site for infection. In terms of preventing it from getting worse, I would think about what flooring you have around for your rabbit. The foam bath mats work well. I personally have .5in memory foam for one of my rabbits who was at this stage and we were able to get it to callous with the floor change. Making sure your rabbit is healthy weight and getting plenty of exercise will also help.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.