As a note, the CA Dept. of health and Human Services does have law enforcement officers. Their primary duty is not traffic enforcement, but they are lawfully able to act on public offenses committed in their presence as any other officer. They are trained identically to local law enforcement and possess peace officer status throughout the state of CA. Most HHS investigators are prior police officers or sheriff's deputies so they tend to have experience in traffic matters as well.
Assuming that the officer that cited you was with the CA DHHS and was a sworn investigator for that agency, then his authority is not in question. His training and experience in the estimation of speed might be an issue, but his authority should not be.

