This sounds fishy.
Who forgets they have a loaded gun in their carry on?
Back in the day, before the TSA and all that federal "professionalizing", I had a vehicle break down in Ft. Worth and I needed to get back to Oklahoma City. I always carried when on the road so my revolver was in my bag but I didn't even think about having it when I headed to catch a Southwest flight. The bag was able to be a carry-on and the screening at Love Field caught it. The screener allowed me to run it back to check into regular baggage. Saved my a$$ for sure...