I have a fitbit here, though I use my Galaxy watch. Anyways there must be one around you somewhere that's not been setup. Unfortunately you will have to wait until it dies (if you can't find it to turn off) or just turn your Bluetooth off. I would just power off my fitbit when that happened.
I tried that earlier, but it doesn't show on the list as trying to pair, but there are three available ones on the scan that I can't do anything with, block delete etc