page's argument is that waymo as a whole was successful, so waymo as a whole got paid a lot. because levandowski was an early waymo employee and pretty senior, he had a large 'stake' in waymo's bonus payout.
however - and this is page's big point - that payout has little to do with his overall contributions to the project, and rather that he had early responsibilties and stuck around.
I'm guessing it was tied to shipping that autonomous car with no steering wheel that they made awhile back.