(written from a Production point of view)
A station chief was a function only mentioned in the script of Star Trek, not in the final movie. In the script, as James T. Kirk and the original Spock arrive at the Delta Vega outpost, they meet Keenser and Spock asks him if he is the station chief. Keenser answers in the negative and leads the duo to Scotty, implying that he is. The lines might have been cut as part of the wider effort to change Keenser into a silent being. The term station chief is a real one often used in the context of colonies and outposts.