Jerry Brown was a conservative by any historical understanding of the term, and he won in a landslide. Gavin Newsom is also relatively moderate. For example, he's made it clear that it's simply not economically feasible to throw money at homeless housing (because he literally tried that in SF as mayor). And hit the pause button on high-speed rail (which is basically a death sentence). Newsom rose up through the San Francisco Democratic political machine, which while liberal on social issues has been until recently predominately controlled by right-of-center politicians and interest groups. The last three mayors, including Newsom, have been opponents of the self-styled "progressive" faction. Unfortunately, Newsom has ambitions for higher office so he's not providing much leadership at the moment; just refereeing squabbles and trying to avoid bad press.
A large contingent of Republicans wanted the top-two primary system, believing it would benefit them. (Though the GOP opposed it.) It didn't work out that way. But it didn't really change the dynamics in the other direction, either; that train had been accelerating for years.
California is a one-party state because of term limits. Running for office is expensive and difficult. Few sane people, unless they're independently wealthy, wish to expend all that time and effort to serve a mere two terms. They want a political career. With term limits the only way to have a political career is to jump office every two terms. The best chance of accomplishing that--of achieving career "progression"--is to work closely with a political party, which can ensure a spot in various low-level offices if you don't make the cut for a bigger office. Term limits make the party system more important. What ends up happening is that the party with more offices and better electoral chances in the near future when this process starts will quickly build on that initial advantage, while the other parties will quickly wither. If Texas enacted term limits I have no doubt that Houston, Austin, Dallas, etc, would quickly become, nominally at least, Republican.
That said, California may be a one-party state, but there are absolutely liberals, moderates, and conservatives within the party. What difference does the label "Democratic" or "Republican" make, so long as there are free and open elections? From a foreign country's perspective, most American politicians behave alike regardless of whether they're Democratic or Republican.
One benefit of being an all-blue (or all-red) state is that there's less political grid-lock. At least, less grid-lock from naked partisanship. Grid-lock from the electorate demanding conflicting and contradictory policies... alas that doesn't go away.