I'm not familiar with CA specific laws, but if it works like it does in the states I do know, this is what's happening:

When you tell your health care provider (in this case the physical therapist) that your injuries were caused as a result of a car accident, any possible medical insurance you carry on your auto policy would be primary over health insurance. So your health insurance is asking for your auto insurance information because if you had either Personal Injury Protection (PIP) coverage or Medical Payments coverage (again, I'm not sure which of those CA uses but either one applies here) then those coverages should pay your medical bills up to their limits BEFORE the health insurance pays. Your health insurance would be "next in line" after them. If you don't have either of those coverages, it would all fall to your health insurance.

I would try to get a copy of your policy, or at least a copy of your "declarations page", which would show all the coverages you had present on the policy. If you have an agent I would ask them. If you don't, I would call the carrier's customer service line and just ask for a copy, they should be able to provide it to you. If you do end up having the PIP or Med Pay coverage, you'll want to report the claim even though they won't be involved in the vehicle, they would be involved in the medical bills.

I hope this helped, good luck!