April is a big month for state tax collections for obvious reasons. In prior months, revenue had been somewhat below budget projections, but April went above projections, more or less washing out the prior deficiency. The Legislative Analyst's Office (LAO) attributes this pattern to the change in federal tax law that affected the timing of payments to the state. For more information, see: https://lao.ca.gov/LAOEconTax/Article/Detail/360
Note that the governor's May Revise is due this month and is likely to reflect the news that, except for timing, things are on track.