You misinterpreted what you saw. I fly a lot and most airline gate agents are quite strict about enforcing carry-on bag limits. They frequently pull passengers

You misinterpreted what you saw. I fly a lot and most airline gate agents are quite strict about enforcing carry-on bag limits. They frequently pull passengers out of the boarding line and force them to gate check extra carry-on bags. The only common exception is for medical equipment needed during the flight.