I'm thinking what happened is that he thought the confidentiality agreement was a little more airtight than it was and that he'd never be challenged on the details.
Can you point me to the details? Sexual harassment is a VERY broad accusation. Women have filed sexual harassment complaints because they thought men looked at them too long or in a sexual way... they "perceived" S/H so it was treated seriously whether it was true or not. Complaints have been filed because a man told a woman she looked nice in a particular outfit. OTOH, bosses have demanded sexual favor for advancement, told offensive jokes, or punished people for things related to sexual/romantic relationships.
The first thing most S/H prevention trainers say is "Sexual harassment is in the eye of the potential victim".
Without the details, what are you going to deny or not deny?