I agree that players care about money, even if it doesn't move the needle in terms of their lifestyle. And I also doubted the face value of that Weetbix number when it was mentioned. Giddey's profile in Australia relative to other sports or even other Australian NBA athletes wouldn't be that strong.
I don't think this was anything targeting the agent or a particular effort from the girl to extort. More likely just someone in her wider circle who got the content and tried to stir things up as payback for something. Occam's razor, etc.
Giddey or a representative probably said to the family a longer form of "Sorry, genuinely didn't know her age at the time. Obviously the future of your daughter is of critical interest to you. If I can contribute to help with PR professionals for damage control to protect her reputation, please let me know." Then wait and see how the family expected it to play out. If they're sane (well, IMO), they take the PR retainer, suggest their daughter be more mindful of social media, put the money aside for college, Giddey pulls his head in after dodging a more major crisis, the Thunder and NBA wait out noise. (All this assumes the story is remotely as we've heard it and not a bigger age gap, etc.)