Rick's Renaissance Walk podcast states that the Via Calzaiuoli is closed to traffic. This has changed. It is open to traffic.
The best place for your valuable feedback is at https://www.ricksteves.com/forms/guidebook-feedback-form
Did you see a lot of traffic? Certain vehicles are permitted in the pedestrian zone: http://en.comune.fi.it/OLD/mobility/pedestrian_zones.html.