Outside of IRROPS, which is probably the case...GoJet is HQ'd in STL and PIT does see its share of CRJ-550s. My guess it was sent back to 'base' for a maintenance or repositioning. With PIT (and others) having extra -550 service this year given the not-daily, point-to-point vacation routes like MYR/HHH/PWM, I'm sure the occasional -550 gets off a normal schedule.