I venture that most horses show some sign of lameness on a small circle on ashphalt…a 2 out of 5 might not sound so bad, really, unless you are looking ahead to Rolex or Spruce International.
I sold an eventer once who was very mildly off on the concrete circle - he went on to Advanced and retired sound…the party made a judgement.
If a horse has large feet, this will put pressure on the joints and that is all it takes. Do it extensively, and the horse can pop a splint.
There are vets around who will not stick their necks out for anyone or anything and they become well known for being able to find some little thing wrong with every horse, and will not commit to ‘sound for purposes the horse is going to be used for’.
I agree with ALL the posters, not your responsibility.