I think his point is that having a "working understanding" of stuff isn't good enough anymore. It's not that you're stupid, it's that things have gotten so complex that everyone is a specialist. Back in the 50's if you were a good mechanic you could work on any vehicle, and make it work with baling wire and duct tape if the real shit wasn't available. Now it's getting close to the point where mechanics have to specialize on a specific brand of car because they can't afford to have all of the electronic diagnostics and the specialized tools that are required for every brand of motor vehicle.
It's the whole "no one person knows how to make a pencil" thing. Our technology is so complex and dependent on so many people all over the world than in a real near extinction scenario a stunning amount of it will be lost and unrecoverable. Just the fact that no one is building spare parts will mean everything will stop working within a few years and you don't just need to go find the place where they built the spare parts, you need to be able to make steel and plastic to make them out of and the people who know how to make steel don't know how to do it in the medieval way, they know how to do it with massive machines and huge amounts of coal or natural gas and electricity which are also not available anymore. We wouldn't be back to the stone age immediately, but even getting back to the middle ages level of tech would take a while and no one will be building an iphone for a few hundred or thousand years.