The best data we have at this point is from China. They have 81,000 confirmed cases to date, most of them happened over an 8 week period. Obviously not all cases of the virus were confirmed but people were hospitalized and tested aggressively.
Even if only 10% of the cases in China were confirmed (and 10% is a low guess at the percentage that might need to go to the hospital with serious symptoms, and thus be confirmed), that means under a million cases in a population of 1.4 billion.
California's population is 35x smaller than China's but Newsom is predicting California will have over 25x more cases.
Sure you can argue that China is lying about their cases (WHO disagrees). Or that they are authoritarian superhumans with a superior response. Or whatever. But this discrepancy is just too big to make sense. I don't think CA will have 25 million cases in 8 weeks.
I think he is trying to scare people into staying home. Staying home is still a good idea, because the health care system will collapse at a lot fewer than 25M cases in 8 weeks. But I think it's fearmongering.