If your iPad is turned-on and participating in Apple's FindMy network - even if Airplane mode is active - it can be detected by other Apple devices that are themselves active in the FindMy network. In this situation, the iPad will still have its BTLE radio active.
Other devices within range of your iPad will detect and anonymously report the detection to Apple's servers, along with the location of the detecting device - which will be only a short distance from your iPad. You should note that this does not provide a continuous tracking capability - but will identify where your iPad was last within range of another detecting device.
More information about using FindMy can be found here:
Use Find My to locate your lost Apple device or AirTag - Apple Support