You're right, La Niña generally means less precip for Central and Southern California, but not always. Looking at the 20 strongest La Niña events, about 13-14 of them were drier-than-average overall in much of California. The La Nina winter of 2016-17 (too weak an event to make the top 20) was also very wet in California, and Tom provides an overview of that winter in this post. In short, this winter has been unusual so far, but not unprecedented.