There is some polyurethane that contains PVC - PVC produces hydrogen chloride which is why it’s always good to have the SDS or know exactly what it is you are cutting. Buying products that are already marked as laser safe means offloading that responsibility to someone else - which is totally valid,
Not sure what the video said before and after the polyurethane comment, but it might be germane to the question.
Also - all polyurethane is bad for the lungs, so be sure to have good ventilation that doesn’t dump straight into an area where people are!