It shouldn't show missionary there (and it doesn't show for me). You can never build a missionary, only purchase by faith. There's really no way how to allow building of religious units, no special ability of a civ, no policy, no wonder effect, no city-state suzerain bonus, nothing. There are multiple ways how to make it possible to buy by faith stuff that can normally be only built (or purchased by gold), but not the other way around.