The article links to https://usa.streetsblog.org/2016/06/02/why-helmets-arent-the..., which positively correlates helmet wearing with fatality rate. Of course, correlation is not causation, and you could logically argue that most of the causation is the other way around, i.e. an unsafe biking environment induces wearing helmets - but at the very least wearing helmets doesn't seem to solve the issue.
The part where the other direction of the causation probably crops up is that, when a society focuses on wearing helmets for biking safety, biking safety will be lower than in societies that focus on biking infrastructure.
The part where the other direction of the causation probably crops up is that, when a society focuses on wearing helmets for biking safety, biking safety will be lower than in societies that focus on biking infrastructure.