In general terms, 9545 is a bit of a strange number to start at for a brand new camera. It's possible that the camera could have continued numbering from a photo that already existed on the memory card, however if you purchased the memory card at the same time as the camera and formatted it in the camera before taking any photos, this seems rather unlikely.
The usual way to check whether your camera truly is new would be to find the shutter count reported by your camera to see the actual number of photos it has taken. Unfortunately it's not possible to view this information directly on the Canon 80D.
The easiest method would be to try uploading one of the photos you have taken to a website such as CameraShutterCount, but (as noted in Michael Clark's comment) this method only works if the manufacturer provides the shutter count in the exif data encoded into the image which Canon apparently don't for the 80D.
There are some alternative suggestions for how to get the shutter count for the 80D in the question linked from flolilolilo's answer if you really want to look this up, although it seems Canon don't like to make it easy, so it's a good thing you were able to figure out what happened.