Unless you used the same assessor, there is no comparison to prove racism. The first assessor might have arrived at the same figure with a white owner. CA has pretty strict rules on assessors, and he/she will have to provide the comps, measurements and analysis used to arrive at the figure.
20 Years ago, assessors in CA just valued the house at whatever it was selling for to ensure the mortgage was approved. If they didn’t do that, realtors didn’t give them business. Now it is quite regulated.
It was the same assessor and only a few weeks apart. Sloppy worker if you can’t remember the previous assessment or check your records.