Only explanation I have is that since this is a bulkhead seat with bassinets there's either a party that requested bassinet use or a passenger with a service dog traveling on this flight, but then the system should have you booted out of 20C completely and the change reflected in your PNR. Looks like an AA IT glitch....
Only advice I have here is to get to the airport as early as possible. The counter opens at 7:30.