Zero-Bug does not mean writing software without defects - that's impossible, instead it means correctly classifying bugs and then striving to keep the bug-count at 0.
I've written another article on the three types of bugs, and one of those is the "unknown ones" you refer to. There are things you can do to tease out some unknowns, but of course there's no cure for bugs as a whole. It's here if you're interested: https://goo.gl/TlvNcY
On the clickbait, I assure you it's not. I labelled the approach Zero-Bug long before writing the article. It creates an attitude in a team. After I've worked with teams to clarify what Zero-Bug really means, they strived towards doing more checks before even pushing out code. We celebrated Zero-Bug days when we were actually down to 0 and believe it or not, I've seen up to 2 iterations at a go be free of bugs. Coincidence? I don't think so.