You're citing a procedural detail that I don't think really supports the claim that his termination was unlawful.

All that section says is that if the guy files a claim with the labor commissioner for wrongful discharge, then the commissioner can "take assignment" of his claim, meaning they can sue the company in his name. It doesn't really say anything about whether his firing was OK or not.

A better reference on at-will employment in California is at http://business.ca.gov/StartaBusiness/AdministeringEmployees....

Edit: s/employment/discharge/ (doh)