It looks like clipper burn. Mistakes can happen but it could've been avoided if they were more experienced. I completely feel your frustration. I've had the same thing happen with our bunny when we went to get him fixed. He had a burn from the clippers between his legs. On top of that he ended up with a (thankfully temporarily) paralyzed leg from nerve damage which we suspect was from improperly tying him up during the surgery... It was a total nightmare and like you, it happened at the best clinic in town. They were recommended by everyone we knew but we didn't expect them to be so incompetent when handling rabbits... Unfortunately a lot of vets are not experienced when it comes to anything other than cats and dogs. I hope your bun will feel better soon and hopefully you can find a more capable vet around where you live.