Hello @Emma4536 ,
Something is really not right here. There is no rule that says dummy cameras are allowed. Do you have that in writing? Because here is what Airbnb’s policy actually says:
Hosts are not allowed to have security cameras and recording devices that monitor any part of a home's interior, such as the hallway, bedroom, bathroom, living room, or guest house, even if they’re turned off or disconnected.
You really should reach out to Airbnb again. This is something that should have been reported to them as soon as you discovered it during your stay.