Or in layman's terms: find a legal grey area and become a billionaire before it becomes illegal.

Was it Ford that said: don't ask me how I made my first million?

What AirBnb did was not find a grey area; unregistered bnb's were already illegal at the time. They simply relied on their hosts facing the primary brunt of the legal and fiscal penalties.

What did Ford do?

Don't ask me, ask Ford! :-p