Yeah, I wouldn't put too much stock in a program's board pass rates unless they are FAR below the mean. For the most part, EM residents are highly motivated and will score well - this is why you have been chosen to interview. I am not aware of any magic recipe for didactics that is solely responsible for a magic board score in the top 10%, but I do know PLENTY of residents who work hard on their own and score very highly. I would take the score average with a grain of salt.
Also, keep in mind that these averages fluctate greatly per resident. For example, your program might have a minimum score required to pass your residency. Your classmate might make that score the first year he takes the test, and then not study as hard for the inservices test for the rest of residency, and have low scores for the remainder of their residency...