What research?
The rest of the article doesn't support the claim that helmets 'increase the risk of injury'. At worst he says cars drive 3" closer, but that doesn't necessarily translate to head injury.
If they drive closer there's increased risk of collision, especially if the cycle has to swerve arounf a pothole, increased risk of collision means increased risk of injury.
Given that with the fact that cycle helmets are not designed to offer protection at speed, then the risk of head injury is obviously higher.