It's the striker strip that can be used in producing meth. The strip contains red phosphorus. Strike anywhere matches are the only kind that don't need a special strip. The strike anywhere kind were probably restricted due to their sensitivity to shock and friction which makes them more useful and more dangerous than safety matches.

I am not aware of this being a regulatory matter in any state, California included. Retailers choose not to carry them because they are expensive to ship due to their hazardous materials classification and an attractive theft / crime target due to their (inaccurate) drug association, but it hasn’t led to any blanket regulation at any state level that I know of. I do think they’re banned from workplaces in California though, but that’s because they’re dangerous, not because of meth.