The viol (Italian viola da gamba) and the guitar are descended from the vihuela, which probably came from Africa/East through Spain and the Moors.
The vihuela de mano becomes the guitar. To play with a bow, it was turned through a right angle and played vertically (all pitches) between the legs or on the lap, hence 'da gamba' (leg) as opposed to 'de mano' (hand i.e. plucked).
Now, viols are fretted, like guitars and have 6 strings. Then we have lutes, also fretted, initially with 6 courses, later with 7,8, 10, 11 etc.
So, what we seem to have here is someone turning a "guitar" round (possibly due to comfort of the left arm position?). The fingering in the left hand is like lute or viol playing. The use of the spike will be because a guitar is not shaped to be held between the legs, so it's been given the cello treatment with a spike.
I have a friend who is a guitarist and they can no longer play some larger guitars because of the positon that puts their left arm in.
Did you notice how the stand attaches to the soundboard? My initial thought was that it would stop it from vibrating properly and kill the sound. But I'm thinking it's transmitting vibration through to the top of the box on the floor..
Yes - a lot of cellist's do similar - the box helps the sound project.
If you showed his left hand position to a viol player, without showing the instrument, you would say he's a viol or lute player - the hand position is the same (which is slightly different for cello - the elbow is higher).
I've just had a thought, given the 8 courses - is this a guitar interpretation of an 8 course lute, but played 'da gamba' because of the width of the instrument?