Please explain, exactly, how I have a "reading comprehension problem".
Just because you went back AFTER accepting the payment from the other party and THEN made the statement that you "don't consider them sold" does not get you off the hook. You agreed to sell them to James.
Probably, what you *should* have done was refund the other party's payment and honored the sale with James... but you did not, hence his dismay.
Look, I get it that it is only hamburger money but that's not the point. Even an admission that you caused this, however inadvertently, would likely have smoothed things over with James... but again, you didn't... instead you staunchly defend that you did nothing wrong, made no mistake, have no responsibility, etc... and insist that anyone seeing it differently is somehow mentally challenged - which is absurd.