Did not expect this post to get all this attention. I've done a little digging and found the operator on X. Had some DMs and he(?) said that they've had 1 black box and 3 white box audits. I'm not going to speak for anyone, so maybe you can ask them directly.
I don't really care beyond continuingto nudge people away from this idea of "seal of approval audits", which have been an industry curse for decades. I don't think E2EE email is a good idea to begin with.