The things some "artists" get up to! Destroying a nice Bechstein by reducing it to a "sculpture". What a waste. Makes you sick. One hopes it was a clapped out old one which nobody wanted because it was beyond economic restoration. Even so, there must be lots of people out there who wouldn't say no being given such a thing for free. OK, rant over.
That said, it's kind of interesting that although the strings for the middle couple of octaves had to be taken out, it was not the case that the keys associated with them did nothing. They could (and were) used for percussive effects.
The greater technical challenge for the performer in these circumstances, I would guess, is coping with the playing attitude of the fingers, which have to jab "forward", in line with the forearm and hand, instead of operating "down" at right angles to them. Quite awkward for chords involving different length fingers.
However, I think the aspect of reversal, with the higher notes being on the player's left and the lower ones on his right, would prove less of a brain challenge than you might think, given a bit of time to get used to it. Although we're accustomed to "left means low, right means high", we are capable of mentally decoupling the link between player's left and piano's left. Compare the concept of "stage left" in the theatre being that side which the audience sees on their right. Compare port and starboard on ships. The starboard side is on the right only if you are facing forward.
To see how easy it can be to play back to front, you could simply try it. Just close the lid of your grand and climb up on top of it, lying on your tummy, and ....
No, only joking. But here's what you can do: Pick a simple tune which you can play with two fingers (one finger of each hand), for example Happy Birthday, or one part of one of Bach's two-part inventions (numbers 1, 4, or 8 would seem suitable). Now stand (or sit) at 90 degrees to the keyboard, with the piano on your left, so you're facing towards the high end. Play. You should find this relatively easy because there is a mental association between the concepts of forward, up, and right, so you move your fingers forward to play higher-up notes.
Now for the next step: Turn around so that you are again at 90 degrees to the keyboard, but now with the piano on your right, so you're facing towards the low end. Play. This should be a little more difficult at first, because you are moving forward to play lower-down notes. But soon you'll re-learn to associate the higher-up notes more with the starboard side of the piano than with any direction relative to yourself. That done, the mental leap to 180 degrees should be doable. If you have access to a flat keyboard which you can simply stand on the wrong side of, you'll soon get the hang of it. Playing anything difficult that way is another matter, of course.