Sometimes second interviews are given by Admissions Officers when further information on an applicant is needed. The AO is basically fact-checking, or gathering more information, trying to decide if an applicant merits bringing before the whole committee. Sometimes second interviews are given by Admissions Officers because the first alumni interview was inconclusive or somehow lost.
From the sound of the email – “fourteen Long Island students have a second interview” – it sounds like a localized issue, meaning the alumni that interviewed you somehow messed up and the Admissions Office wants to make sure they don’t over look anyone. That would be my take on it. I wouldn’t take it as a positive sign, but another chance to sell yourself.
Best of luck to you and the other 13 students from Long Island!