I don't have the citations to back this up anymore than you did, but it was also passed because of the rise in Black Power movements walking around with guns.

I used to be an obnoxious gun control advocate until I learned that California's gun control legislation was brought about in response to the Black Panther's patrolling predominantly black neighborhoods while armed to protect the people of the neighborhood from state sponsored (police) violence.

Reference to start from: https://www.kcra.com/article/liberty-limits-black-panther-pa...

This topic is full of subtlty so recommend reading the sources from that article and so on.