I will agree that there is no legal requirement for the car to be "insured", but there must be "financial responsibility" that is in effect "for the vehicle". For the vast majority of privately owned vehicles, that "financial responsibility" takes the form of insurance.
This is from your own link:
16020
(a) All drivers and all owners of a motor vehicle shall at all times be able to establish financial responsibility pursuant to Section 16021, and shall at all times carry in the vehicle evidence of the form of financial responsibility in effect for the vehicle.
You can try to play with the words all you want, but aside from the fact that "insurance" isn't the right term, the fact is that the vehicle must, "at all times" be covered by some form of "financial responsibility".
Furthermore, at no time did I state that comp/collision was legally required (not sure where you got that from).
Lastly, you state that you've never had to provide proof of "insurance", but you were required to show proof of "financial responsibility", which
, as stated above, is usually insurance. For many years, such proof has been transmitted electronically to the state by the insurer, so the prior way of doing things may have slipped your mind. For the past 30+ years I have overseen the registration of not only my own personal vehicles, but a sizable fleet of corporate vehicles as well, so these things are pretty fresh in my mind.
You should probably review the link I posted, as it is a link to the California DMV's web site relating to financial responsibility. I've typed it out here instead of allowing the forum to reduce it to a link. Granted, it's not a word-for-word recitation of the law, but it will help guide you (and it IS published by the DMV, as I pointed out above):
www.dmv.ca.gov/portal/dmv/detail/pubs/brochures/fast_facts/ffvr18