Is “flatfoot” here mean a police officer? If so, why does it mean that? Or does it mean something else?
Yes, you are correct, the term "flatfoot" here mean police officer. "Flatfoot" is slang that is used for police officers, especially those who have a foot patrol. It is most likely related to the large amount of walking that foot patrol police officers have to do. It is not usually used in a positive way and may be considered offensive to some people. Ex: All you flatfoots do is hand out parking tickets. You're not real police officers. Ex: I've never wanted to be a flatfoot.