This Articel is bullshit. Helmets make cyclist more safe. It only reduces the total number of cyclist. And because of that there is less investment in cycling infrastructure. But the scientific articel they are linking to says following

" Do more people on bikes cause cycling to become safer, or does safer infrastructure attract more people to bike? There’s no conclusive evidence either way, but the answer is probably a mix of both. "

So full blown clickbait...