...but can also be taken to mean something that is "set in front (of something)", which would be the sense it's used in here. Nouns ending in -er work like that in German.

Oh, and what "Vorsetzer" actually means in German, IIRC, is "tray" -- the flat thing you carry around coffee and cups and stuff (or whatever) on, in order to serve it to (=set it in front of! :-) someone.

HTH!