Something is odd there.

Normal reasons for /3 wire on a receptacle run: 

 - Half-switched outlets (tabs broken, 0V between black&red, or perhaps
   phantom voltage between the switched conductor and neutral or unswitched if the
   switch is off)
 - MWBC (tabs broken, 240V between black & red.)

In either case, black & red would NOT normally connect to the same terminal. Since the breaker didn't immediately trip (sign of an MWBC without the tabs broken, or with black & red connected any other way), look for a switch that will seem to "do nothing" because the switched and unswitched hots are currently joined together.