As it appears from the audio that these were the only aircraft of frequency at the time, what was the rush? Is SW one of those airlines that has tight schedules, and usually scoots off at high speed as soon as the opportunity arises? That might have influenced the controller's 'thinking' more than the impending arrival of the Fedex ... a sort of automatic reaction.
Not excusing the controller, just trying to get my head around "WTF was he thinking?".