If, as you suggest, it is a site safety rule and they breached it they were lucky. Such a breach normally leads to loss of job in the construction industry. I would certainly have considered it.
Next time you go past a big site take a look at the site information signs. I'll be surprised if there's not one along the lines of "No hard hat/ear protection/ high vis - no job".
Very few small/medium enterprise construction contractors continue to trade for very long after a conviction for an H&S breach.