Is it true you can't have ferrets as pets in California?

True. They are 100% illegal to import, transport, or possess. They are illegal because the Fish and Wildlife officials have determined that if they were released into the wild (as irresponsible people are likely to do when they decide they don't want them anymore), they have a high likelihood of surviving in the wild and could endanger native wildlife.

true there illigal in cali

Yup, its true

It's true, and it's because of not wanting to contaminate/endanger the local wildlife, if certain mammals (including ferrets) were accidentally or purposefully released into the wild.

they are illegal in CA under Fish and Game Code Section 2118 and the California Code of Regulations

You can have ferrets! Why else would they sell ferrets at local petstores? Including select petcos most of the time! :) Whoever told you that is wack.