In the Educational Round 171 my friend https://codeforces.me/profile/KushKushal got a rank of 555 out of 10900 official div2 participants and got a performance of 1991 and my other friend https://codeforces.me/profile/arnavra3 in the codeforces round 983(Div.2) got a rank 515 out of 14500 official participants got a performance of 1981 only even though there were more official participants and he got a better rank?

Could anyone tell me how this works?