I can only imagine the reasoning given by the talking head who recommended it. Mine would be that covid-19 is spread through the respiratory droplets which dentists have routine intimate contact with, that they may have treated someone who is asymptomatic but capable of infecting others, that their office disinfection procedures are less than perfect and that I'm in a higher risk age group than average.
I suppose dental office visits these days would screen with questions around recent travel history, any respiratory health concerns, and a quick temperature check.