I thought at the time and still do that that was a post priori justication. The real important steps were in closing schools, in curtailing public transport , particularly the underground, and social gatherings eg pubs, football matches, horse racing.
It is noteworthy that evidence is emerging that personal services eg nail polishing, hair dressing were very serious vectors. The California outbreak being identified as a nail salon...Two people within arms length for an extended period.
Just picked up on a scientific paper with the following facts . An average virus shedder is outputting 7 million copies of the virus in every millilitre of liquid from their lungs , but outlyers might be 1000 times more potent. . That droplets with a probability of 30% of containing a live virus can persist for 8 minutes in still air and circulate, before either dehydration, and presumably becoming non viable