This is exactly why you never want to half-wheel or ride aero bars in a group. Bad things will happen!
Half-wheeling is the act of riding with your wheels overlapping. You may say, hey, even the pros half wheel. Let me assure you that professional cyclist have incredible reaction time and have the ability to avoid touching wheels with another rider.
You may also say that this happened by accident. Well, if the rider was not on his aero bars in a group he would have more control over his bike. He may have been able to break sooner.
So remember, no half wheeling.