So if I’m understanding this right: Both players saw that the position was drawn anyway, no matter what the promotion was (if it were anything but a bishop, the king would have taken it), so there was nothing lost by having a little fun.
This one, though, was genius, even if it’s a trick that would never work against a human opponent. As I’m reading that, the computer was programmed to never accept a draw, if it thought that it was in a superior position. So the human player arranged a sort of pawn-zugzwang, or took advantage of one that arose naturally, where the first player to move a pawn would be put at a disadvantage. He then deliberately sacrificed some material to ensure that the computer would think itself superior, and started wasting moves. At 49 moves after the last capture, the computer felt itself compelled to move a pawn, so as to avoid a 50-move draw, which resulted in the whole board falling apart in such a way that the computer’s material couldn’t save it. At this point, the human decided to insult the computer in a manner which would be a horrid breach of etiquette against a human opponent, by winning with a whole bunch of bishops instead of going in for the clean kill.
I had actually considered the possibility of underpromotion as a deliberate insult, but discarded it on grounds that no serious player would be that unprofessional. I hadn’t considered, though, that etiquette wouldn’t apply to a computer opponent.
And I was also, of course, aware of constructed problems where this either has already happened, or is forced to happen. That’s why I put in the “competitive match” qualifier.