This is case is about suing a donor-advised funds though, so I'm not sure it's particularly relevant.

This ruling is fairly specific to its facts, and is about a particular cause of action (financial mismanagement). While donors don't have standing for that cause of action by statute, it appears they do for breach of fiduciary duty: Cal. Bus. & Prof. Code § 17510.8. And that's the only CoA where they're relying on CA nonprofit law.