Im so confused

i played my friend in a 1v1 to see wether or not i was good enough to join his team we loaded up a game and i was karma aginst his lee sin not only was this a very big advantage to me but when i beat him he said i was really good even though i felt i played REALLY badly in that game also i wanna mention hes been playing since season 1 and i started in season 5 but apparently he thinks im good? i dont understand