CA employment law does not allow a company to universally ban moonlighting and fire you unlike most other states. They can only do that if it interferes with your work, or it creates a conflict of interest
Do you think that an Uber driver driving for Lyft can be construed as a "conflict of interest"?
Even if not at the same time, if Company A is having to pay for the vehicle or whatever other costs and equipment are being used - in what world can someone driving the comcast truck start installing for AT&T?
This logic is so twisted.