It's only a 'mistake' in that he regretted the decision because it had a negative impact on some other values he held - Had it been the case that his distaste for skeptics outweighed his values to be liked and/or to sell more products (or whatever other considerations made him change his mind) then he would have persisted with the sign and would have been doing no wrong by it, after all this was his property and it's fully in his rights to determine the use of the property including who is allowed on the premises, irrespective of what other people may think of it.
So even if he hadn't had conflicting values that eventually overturned his initial decision, leading to him later apologising (likely seeking to recover some lost value in the form of customers or social standing) he'd be doing nothing 'wrong', he'd just appear to be a 'bigot' to a certain subset of the population and if that's the price he's willing to pay for excluding this subset then that's his decision to freely make.
So even if he hadn't had conflicting values that eventually overturned his initial decision, leading to him later apologising (likely seeking to recover some lost value in the form of customers or social standing) he'd be doing nothing 'wrong', he'd just appear to be a 'bigot' to a certain subset of the population and if that's the price he's willing to pay for excluding this subset then that's his decision to freely make.
.
