Date: 202103
Location: ZZZ.Airport, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Flight Attendant (On Duty)
Reporter qualification: Flight Attendant Current
Human factors: Confusion; Communication Breakdown; Other / Unknown; Time Pressure; Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Passenger Misconduct
Detector: Person Flight Attendant
When detected: Aircraft In Service At Gate
Result: General None Reported / Taken
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Human Factors

Narrative: I was thanking passengers as they disembarked onto the jet-bridge in ZZZ; and I was trying to call rows to deplane on the PA. The cleaning crew were at the front door (1Left) trying to get on the plane while the passengers were leaving; and the pilots were also trying to gather their bags and leave. This made the situation very chaotic. I was not aware of it being a 'quick-turn'; as I am always happy to try and help out with the quick-turn cleaning.The cleaners slipped on a few at a time; in between passengers leaving. I saw the two aft crewmembers with their luggage; and moving forward through the cabin; towards me. The cleaners were already onboard; cleaning throughout the plane. I said; 'last but not least!' to the final passenger; thanked her and gathered my belongings. I looked back and only saw the cleaners; and my crew who were almost to me. I didn't see any more passengers and thought we were done. I double-checked my doors and the forward lavatory and stepped off the plane. When the aft crew stepped off; there was a male passenger with them who had been mixed in with the cleaners. He did not have his boarding pass with him. He said he wouldn't leave without it; and that his seat was XX6. He wanted to go look for it himself; but crew went to look. His boarding card was found under his seat.A contributing factor is having so many people onboard/in jetbridge and the cleaning crew coming onboard (sometimes in just sweatshirts; hoodies; jackets; hats; masks; etc.) and mixing in with disembarking passengers; and vice versa.  Flights are more full now; and anyone can be mistaken for a cleaner.Other factors: double-checking the passengers haven't lowered or removed their masks; as they often do now; as they are coming down the aisle towards me and the boarding door. The passengers are trying to look down the aisle and gauge how far we've gotten with the row announcements to deplane. Also; 2-3 pilots using the lavatory; gathering bags and leaving; while passengers are disembarking causes more confusion. All of this; and the extra amount of ground-staff/cleaners onboard and in the jet-bridge in civilian clothing; causes more confusion; multitasking/load at the boarding/deplaning door.I assumed the last passenger I saw; and said goodbye to; was our final passenger onboard.I would not have stepped off the plane had I known there was still one passenger onboard.I will also alert corporate security to this incident; and the added potential for this confusion during disembarkation.




Synopsis: Flight Attendant reported the aircraft cleaners were slipping onboard to clean the aircraft before the passengers were completely off. One last passenger; resembling a cleaner; remained intermixed with crew and cleaners during the crew's exit.