An employer doesn't HAVE to give you a reason why they don't hire you.
The section of the law you're talking about, is only for INDIVIDUAL health insurance policies, not group health. Already, if you get hired on, the group insurance HAS to accept you.
And it's NOT true, that companies that employ a certain number of people are required to provide health insurance. Completely false. NO company is required to provide health insurance.
So, your whole question is based on faulty assumptions . .. moot point.