The redness looks like slight urate burn, it can happen fairly quickly if the snake is laying in its own waste.
Some snakes just make a mess of their cage and you can't watch them 24/7.

I don't see much swell in the pictures. If this is something you are concerned with: I would check your belly heat source with a temp gun and confirm that it is heating a large enough area in the correct range for the snake to thermoregulate properly for digestion. A snake that is too cold with food in it will bloat.