Ah, the points aren't being counted up yet. I got first all three races, so it should be 30. It's just that their performance is so awful compared to the unmodded version it can seem less than normal. For instance, getting second consistently on three races before Rainbow Road should be getting you 24, which par for course for a rival CPU in an unmodded Double Dash. Also 150cc means you get a heavyweight pair for a rival. Yet these guys got stuck, are 2nd overall, and are using a lightweight kart.