Utter, complete, unadulterated hogwash. In fact, one of the crazier servings of bologna I've ever heard.
If they're going to give out $5,000 fines, they're going to want to have a LAW they can cite that you'd broken. And that one would be...?
...
Now, there's one way this could have some tiny element of truth to it. If the officer did discover that the driver was armed, and was one of those odd ducks with a personal problem with folks being armed, he could have decided to throw the book at the driver for any violation that might remotely stick. Taillight out? Weaving/swerving/reckless driving? Maybe some heavy fine for having the child unsecured. Don't know if that could possibly add up to $5,000, but it could be quite a bit. Now most folks would go to court and fight such a pile of BS charges, and the judge would be pretty likely to throw some of them out. And, if it looked like the cop really did have it in for this guy, the judge might even throw out the whole case with a stern warning to the officer not to abuse his authority.
But that's all speculation.