The article you linked says the individual was from the City of Chicago's Department of Aviation. While you do bring up an important clarifying point, I'd be surprised if the individual in question didn't have most or all of the same authority/powers as a police officer within his jurisdiction.

Some additional information from the Wikipedia article on airport police that seems to be relevant: "The City of Chicago Department of Aviation Police perform safety, security and law enforcement functions at O'Hare International Airport & Midway Airport. The department was formerly called the Department of Aviation Special Police. The Chicago Police Department Airport Unit also performs many of the law enforcement duties in and around Chicago area airports." (https://en.wikipedia.org/wiki/Airport_police) However, that information may or may not be current.