It's so crazy/impressive to me that some vaccines are actually "prefect".
It doesn't need to be perfect at the individual level to cause that - and in fact many vaccines at the individual level actually have pretty bad metrics - like for example only preventing half of cases.
However, note that this is in a population where there will no doubt be leaks. Even if everyone in the area got the jab that doesn't mean they won't have sex with people who didn't. Thus an infection rate of zero is a good showing.