I can't give you a definitive answer on the California Digital Card. I think that is a question you would have to ask the Tour office directly.
Here is the quote from the Frequently Asked Questions section in the Tour Accounts.
"Do I need to bring my original vaccination card with me on tour?
Yes, you may be asked to present your original vaccination card so we recommend carrying it with you when you travel. In addition, you should either scan or photograph both sides of your card and keep the digital copy on an easily accessible device, such as your phone.
Will I need a negative COVID-19 test prior to joining a tour?
Yes, for our tours starting May 20, 2022, and later, we're requiring pre-tour testing with a rapid self-test. Each tour member will need to show proof of a negative self-test taken within 24 hours of the first day of the tour, whether or not a test is required for entry into your arrival country. "
I am bringing one Binax Now (proctored test) in case I test positive along the tour route and need to show an "official test" to my travel insurance. I am bringing 6 other home tests and if I need more (I hope not!) I will purchase there.