I think that as a measure of skill vs. a computer that statistic doesn't tell you all that much. Note that even in that measure Magnus only picks the top move ~85% of the time, and that includes many moves where the top move is "obvious" which will inflate the average a bit. And it needs to be kept in mind that Magnus cannot win against a modern computer, so clearly that 85% only means so much, computer play is still on a whole different level from human play.

Beyond that, time is a very important factor, running out the clock is one of the most effective ways to win against cheating opponents. Magnus only finds the top move ~85% of the time and takes probably 10x to 100x the time to do it. And like the other commenter noted, variance in the move time is an extremely obvious tell. Magnus will blitz out certain moves (even in classical chess) and then think for ~40 minutes in other complicated positions. A computer can do both positions in basically the same amount of time, and cheating players typically don't know when they "should" be thinking vs. playing fast.

Note that even his "top engine match" is 85%. This is not a fantastically high number, given that maybe 40% of moves are obvious/must-moves. I bet I match the engine ~60%.

I also think this is his classical games, not rapid, blitz, or bullet.

Top human players tend to make safer, lower variance moves than things engines prove super safe on evaluation. They may give up a few centipawns for ease of analysis.

And yet time and time again, chess streamers and content producers run across people with newly formed accounts and perfect win records playing the best engine move at regular measured intervals.

If you are cunning enough to hold off on the best move for a few extra seconds to appear unaided by an engine, or if you blunder X% moves in your game (or simply play the 3rd or 4th rated move which still probably wins against most humans), chances are you'd do fine learning some chess strategy and playing the game unaided.

People keep asking why one would cheat at chess. I'm sure there are some bad actors who aim to disrupt the game, in a manner consistent with cheater motivations in other games. I'd imagine many cheaters are simply looking for some quick dopamine after being frustrated by a plateau in their skill.

A random delay is also a tell, though. An obvious move shouldn't take 15 seconds, but if that's what the random delay for that move is, that looks suspicious. A more difficult move shouldn't take only 3 seconds, but if that's what the random delay for that move is, that also looks suspicious.

In general you’re right, but there are some tells because humans don’t have a random delay. It’s connected with the complexity (from the perspective of how humans think, which is different from engine calculation) of the position. One of the things that makes cheaters stand out is they will have a random weird delay on various obvious moves.