Internet bunk.
An Eel's mouth and teeth are made for grasping and swallowing. The simply do not cut and tear... they are incapable due to their mouth and teeth set-up.
If you want to see a thumb shorn off, ask a Shark how they do it. Inscicors, sawing by thrashing. Eels teeth are needle sharp, like a cat's claw, and they are curve angles towards their gullet. They are designed for holding and assisting in the swallowing- nothing more.
An Eel is simply not equipped for this kind of performance.
If you want further proof, look at it the way the experts in video analysis do. It goes from perfect photography to very amateurish stuff. Kind of understandable, experts aren't along 24/7. But....
0-4 seconds: The camera is seemingly haphazardly & amateurishly "pointed the wrong way" (to the right) filming nothing, then- after the "off screen bite" (and appropriate sub-title explanation),
5-7 seconds: the very amateur videographer then manages (under the influence of stress & panic?) to fill his frame perfectly for 2 seconds with the encounter...
7-12 seconds: then somehow the camera swings away again- this time to the left... and remains motionless for at least three seconds.
Sure.
Word is that it was an industrial accident (compressor or outboard?) and a dive instructor made the best story he could- right there in a video camera.
Rant over- Carry on now disregarding the bio-mechanical impossibility of an Eel severing a human thumb.