As Gyngyn said, weak interviews can lead to waitlists or rejections. Many committees have an algorithm that kicks out an overall score for an applicant that factors in things they select for (gpa, mcat, ECs, essays, interviews, etc). It is entirely plausible for interviews to not go well enough to kick someone’s overall score down. An interview invite means someone could be admitted if they have an excellent interview, if on the cusp with other parts of their app, or merely a strong interview, if other factors of their app are stronger. Keeping in mind that schools may admit between 30-40% of their interviewees, a strong interview performance is helpful.