Multiple people in one place can still be completely wrong. Concussive events are what matter when it comes to CTE; many of them occur without physical contact to the head just as impacts to the skull may not have concussive effects on the brain. What matters is sudden acceleration, not contact to the head.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2995699/
[2] http://www.uwhealth.org/sports-medicine/clinic/concussion/11...