Since client owns a home in California and was simply out of state due to COVID, 'temporary absence' it sounds like client will be returning to California at some point. I would report it to California as a full year resident.   Here is Calif Pub 1031 guidelines for determining resident status that should help.  See page 4 defining resident, and page 6 income taxable by California.

https://www.ftb.ca.gov/forms/2020/2020-1031-publication.pdf