Do we have any data on when that affiliate income was earned?
How do you know he got 2 more referrals in 2023, and why does it matter?
Going from 4 to 6 referrals doesn't mean much on its own. He could've earned all that income on only 1 referred user (e.g. himself) for all we know. Unless there's some additional data available of which I'm not aware of, this is nothing to be concerned about.