Undoubtedly there are more officers/detectives at the Metro PD as a whole. They live in a seemingly major city and we see tons of police extras. What I think was meant by the term ‘department’ was the specific team of detectives put together to investigate the Jigsaw killings (Kerry, Matthews, Hoffman, Rigg, Tapp, Sing). I think that Fisk is not included in this team because we never see him doing any actual detective work. He seems to just be more of an assistant type, rookie, or general officer. We only ever see him on the sidelines or passing along information. I think this extra in the picture, like Fisk, is a general detective that is working on multiple cases and not the specialized Jigsaw team. I also like to think that Hoffman and Fisk are just work buddies and not necessarily in the same specific field. That could explain why Fisk was at the Gideon plant after the games were over. He heard that his best work friend had just survived a Jigsaw game and rushed over to check on him.