We can only hope we're not heading for a "nanny state" on HS football fields. What ever happens, good or bad (which depends entirely on which side of the field you're on) during a 5th down, SIMPLY SHOULDN'T HAVE HAPPENED, and the simplest, and fairest, solution is SHOULDN'T COUNT.
Misreading 2nd or 3rd down and misunderstanding it as 4th down, is SIMPLY; A MISTAKE, which could be made by either team, and, like most mistakes, present unfortunate consequences. Football is a wonderful, and often complicated game which requires EVERYONE to pay attention to a lot of different things.
Misunderstanding, or misreading, a Down is one of those mistakes that should ABSOLUTELY NEVER happen to an official or a coach, more than once, because if it happens that one time, it should burn scar tissue deep into your rear end that should NEVER permit you to forget the embarrassment and pain of doing so. Knowing that SHOULD likely prevent that first mistake from happening.
There are always reasons to leave ANY and ALL boxes Pandora leaves around, closed, hopefully our interpreters, and rule makers, will remember that.