I assume he didn't - the point is asking people to wear helmets discourages biking. In practice it's overall healthier to not ask people to wear helmets.
Having visited Amsterdam once, I'm honestly a little surprised there are so few cycling accidents. The number of bikes is huge and the flow of it looked a bit like a controlled chaos.
The Dutch seem to have understood the street smarts and the unwritten rules of cycling (as applies to their environment) really well, so that probably explains it, along with a cycling-friendly environment.
I'm sure it's something that becomes instinctive, and that develops best at a young age even if it can be learned a bit later as well.
I don't know if the environment regarding play is somehow different to other European countries so I'm not sure what you mean with that. I believe engaging in play that tests one's limits without risk of serious injury makes a person more aware of one's body and limits, though, and I find it a good idea, too. I wonder if the Dutch have a different culture somehow in that respect.
I also learned to ride a bike as a child, and so do most others where I live, but the culture regarding what's considered safe or typical cycling is somewhat different here.
I assume he didn't - the point is asking people to wear helmets discourages biking. In practice it's overall healthier to not ask people to wear helmets.