Depending on the application you used to alert you of the AirTag, it’s possible that your phone did not send location data back to Apple.

Apple can track AirTags, because iPhones are programmed to listen for them over Bluetooth Low Energy, and send the ID of the AirTag and location data of the device to Apple.

If your Android phone has an application to listen for BLE devices in the background, keeping track (locally) of which devices it saw in what locations, that application can tell you if you’re travelling with an AirTag (or similar device). It might even be able to interact with the AirTag, such as making it beep or reading its ID. If that application doesn’t send your location to Apple, the AirTag was not able to use your phone to make its location known to the owner.

Therefore, to the owner, AirTags are useless unless an iPhone (or other device that sends its location to Apple) is around.