It could also be someone lifting it off through software on your phone if you had a device with a terrible implementation for handling fingerprints. See this piece about the HTC One Max from two years ago - the fingerprint was stored as a bitmap image in a "world readable" folder and refreshed with the image from the latest touch!

[1]: http://www.theregister.co.uk/2015/08/10/htc_caught_storing_f...