If it's just the combination of your personal experience and an idea, no. As an investor, or developer, or competitor, it's still just an idea. You cannot transfer your deep domain knowledge to me over coffee.
Yes, definitely. If you're talking to an investor, they're not going to be able to fully appreciate a deep domain insight anyhow. You tell them about what they can appreciate: the size of the market, the cost of bringing your product to market, and the problem you are solving for your future customers.
The article implied it was a conversation with a business, rather than an investor.
In which case, you have a different limited conversation for the initial meetings. There's even less need to tell a prospective developer about the secret sauce.
I would say "it depends" however someone without the deep domain knowledge would have a difficult time executing so you most likely don't need an NDA anyway.