If CA sees that you have a mortgage or state licenses of some kind (nursing, hairdresser, security guard, etc) they expect to see a tax return from you or you'll get a letter...its just easier to file for CA, even if its not required to avoid any hassles down the road.

FWIW the chances of them having enough income the last 2 weeks of December to generate a filing requirement is probably slim, unless they sell stock or pull their RMD the last 2 weeks of the year or something like that., BUT if you're filing a federal return with a CA address on it, CA may send you a letter asking if you should have filed a return.