I find the claim particularly hard to believe. I ride at least twice a week with my brother and we behave exactly the same with and without helmets. If you have a habit of always wearing your helmet, it just starts being something you don't even really consider as part of the equation. In fact, we will occasionally go almost an entire ride before realizing that one of us forgot to put on our helmet.

I find it much more likely that claims of "data shows..." are due to uncontrolled confounding factors, such as riders being more likely to wear a helmet when they perceive the ride as meeting a certain risk threshold.