My only possible theory is that... maybe Polly knows? If that O&O backup was canon, Polly has been to Man's World between Zeus' manifesting to her and the amazons all showing up, and at a time and in a place where she could plausibly run into Diana. So, if Zeus told her that they were fulfilling Athena's dying wish, Polly might have passed that along to Diana?
Which again, is manifestly not something that should have happened offpanel.