California Roll is a slur used to describe Asian/white in a derogatory way. Much like the food, a mix of American and Asian. Also Asians, and thus half-Asians are much more prevalent on the west coast than on the East.
The word California Roll is a racial slur that has been used historically to degrade and dehumanize asian/white. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to asian/white. If you are unsure about whether or not it is appropriate to use the word California Roll, it is best to err on the side of caution and avoid using it in any situation.