In his post he links to the Code of Federal Regulations. It allows for mistakes to be made by the business.
This is what I read:
It says: you can't call someone that says "Don't call me"
However, if you have a written policy to try your best and follow the law and generally your business follows the policy, then you are not liable for violating this rule if it was a simple mistake.
So the case of David calling him back a few days later may have been an honest mistake. But the if the business did not have a written policy in place, have training of the policy, maintain a list of DNC numbers, etc. then they are liable for the mistake.
That's how I understand it. So it seems the law is forgiving for businesses that are trying to follow the law. But I am not a lawyer, so my reading comprehension skills are worth very little.