No, it's 250MW of peak power. I'm not sure what the total energy storage capacity is for California, but the typical project has 4 hours of capacity.
For an example please see this PG&E project which is coming online in Summer 2021. These installations have 700MW of power capacity and each has a 4-hour discharge time.
You're right about the numbers, but still this is tiny at the scale of the grid. 2.8GWh is still only around 5 mins of consumption. You would probably need a few days of storage to run a 100% wind/solar grid, so that's about 1000x more.
