Neville, circumference x rpm = linear speed. pi x D= C so a 90mm bit is almost 283mm in circumference. Turning at 12000 rpm, which is about as slow as a router will turn, it is going 3,396 meters per minute at the rim. I would say they were justified to be concerned. I wouldn't want to be riding in a car that was going 3 1/2 km a minute.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.