Different rental locations frequently have different rates, so this is not all that surprising. The computerized reservation program uses a rate-setting algorithm that depends on various supply and demand factors, historical rental demand, and whatever else the folks who created the model incorporated into it. This is quite similar to the way the price of airline tickets can fluctuate depending on demand for seats on a particular flight. Changes can occur from day-to-day, hour-to-hour, and even minute-to-minute. The CCC does not have the inventory of cars that are available at the airport. To a significant extent, the CCC inventory is drawn from cars that were picked up elsewhere (frequently at MCO by renters doing a one-day rental to get from the airport to WDW but not keeping the car during their stay). If existing reservations for CCC pick-up will exhaust anticipated available inventory for the pick-up time you are booking, a car may need to be brought in from another location (like MCO) so the rate increases to reflect the supply (or lack thereof) and demand at that time.
Ralph