I wonder if there is a problem with the data collection at that time? From your link, it looks like to drop much lower than 0.33, lowest value on that chart is 0.11, which is massively lower than any previous worldwide value, before jumping up to ~10.
Wiki Santa Ana winds. They typically bring <10% humidity as they blow towards the pacific ocean. This can happen overnight and you'll wake up with "raisin-eyes".
[1] https://www.weather.gov/wrh/timeseries?site=KSMO
[2] https://www.wunderground.com/cat6/world-record-low-humidity-...