Passer is one of those verbs where meaning depends completely on context, not translation
SI – responding to negative questions
In French, si is used to contradict a negative question (to say yes).
Tu n’as pas faim
You are not hungry
Si
Yes, I am
Tu ne viens pas
You are not coming
Si, je viens
Yes, I am coming
Il n’aime pas ça
He does not like that
Si, il aime ça
Yes, he does
In English you would just say yes, but in French, si is essential to correct a negative assumption