, I understand, there are always two sides of the coin. It is no problem to arrive here and in case the IO spot the problem at airport, they will still stamp him in under the 30 days visa waiver. It is no problem, he will not be detained or send back.
I not argue, I could not care less, but we talk a legal issue. In 99.99% no one will notice and it should not be an issue, but in legal term the visa is void.