Yeah, this--and all the other copycat articles at that time--are bullshit. It absolutely will work with a severed finger. If the first try doesn't work just wet the severed finger with water or take a pencil and color the finger tip with graphite.
Example of someone unlocking an iPhone with the latest and greatest sensor tech (on phones anyway): https://youtu.be/2u4ZLGsw1zo
They had less than a severed finger: A simple silicone copy. Something you can actually manufacturer with a high resolution picture of a fingerprint (as demonstrated by the CCC).
