In traditional provence use case, you want to prove the image have never edited after it was created from the source. When signature mismatch, it is considered invalid.
For AI use case, you want to proof the image have never touched with AI. C2PA only (kind of) proof the last touch wasn't from AI..
Given how bad Google's implementation is, the only thing Google's implementation proves is that someone somewhere on earth owns a Pixel phone... and we'll probably learn that it doesn't even prove that.
I like to contrast how Google has responded to the failure of their implementation with how Nikon responded to the very same sort of failures. (Search for "Nikon" here [0], but -IMO- the whole post is worth reading.)
[0] <https://www.hackerfactor.com/blog/index.php?/archives/1102-C...>