I was a line manager in a hotel years ago. I was always the person who interviewed the candidates, but I was not always the person who made the hiring decision. It depended on the mood of the general manager. Sometimes he was not involved at all, and sometimes he made the decision based on the person's application without actually meeting them. This, after I had contacted and interviewed the candidates.
So if you go on a job interview and think everything went well, and are surprised to find out you didn't get the job, that could be why.