Too lazy to look at panels, but beyond Kuma referring to Vegapunk as a man, what did Caesar, Queen and Judge refer to Vegapunk as, he or neither to keep it a mystery? If they never refer to Vegapunk as a man then perhaps Kuma's memory was altered to remember Vegapunk as a man
Still even then she's young as shit, unless she was a genius since 10 year old or some shit, that theory might not stand.