>California is getting their ideas from WHO:
It says so right in the order for San Diego:
sauce:
https://www.sandiegocounty.gov/content/dam/sdc/hhsa/programs/phs/Epidemiology/HealthOfficerOrderCOVID19.pdf
https://www.sandiegocounty.gov/content/dam/sdc/hhsa/programs/phs/Epidemiology/HealthOfficerOrderCOVID19.pdf