Can you provide a link to his account??
If he knew there was an extra digit on the package, why would he have not said anything then? Most people know there’s only 5 digits (there’s actually like 9 I think) but if I were to give you a 6 digit Zip Code, wouldn’t you ask about it?? Lol.
Also, if the zip code of the package and the state don’t match, I’m about 99% it would raise a flag in USPS’s system upon acceptance into the system.