Ah was hoping I might get to ride with a real trials rider :-) but with work and that wouldn't be able to get over there. I know the bubble a bit, but not been there since getting into trials riding. I expect there's stuff on the sea front with boats and that with potential to look good on camera.
Spiral I reckon is from withdrawing a jammed tool, something bound onto the cutting edge of the drill (diamond) and created the spiral whilst withdrawing it; you could possibly achieve that feed rate cutting into plasterciene or butter
As raised above, there doesn't seem to be an abundance of spiral grooved cores so I suspect it to be an anomaly that can be jumped on to try to cast doubt.
Holes drilling into the tangent corners could be tube drills driven by a short crank, progress would be slower due to reduced possible torque that can be applied but still feasible. The grinding/wearing action of the tube drills wouldn't require high torque compared to cutting the stone (as a modern tip tool does in metals), just a consistent motion.
Ok so you are holding on pretty tight to to the spiral. However, we know that a single turn of the basic tools they had is not going to go through anywhere near enough granite to make the grove in the way you think it’s been made. How many cores show this groove pattern? Is it just this one? If it was all of them I can’t imagine the conspiracy theorists wouldn’t have made a bigger deal of it...
So what are the alternatives?
Crazy tools - no evidence.
Something else - lots of options.