surely they're talking about the opening only, where the best moves have been analyzed to death. once you're in the middle game and it's a position that's new, you play the best moves.
You get to new middlegame positions by playing the sub-optimal/weird moves in the opening that Magnus is suggesting. Otherwise, you get to a familiar middlegame and just grind out a draw.
I don't really understand Magnus' position about playing a sideline vs. Hans Niemann in the infamous cheating game, and was reportedly shocked Hans knew the responses. Before any of that became public and I was reviewing the game, I just thought it was a sideline transposition to a Catalan position, and everyone knows Magnus plays the Catalan as a main white opening - so a weird way of getting to that structure is not that novel.
Hans' explanation made sense, even if he was wrong in his first interview and it came off weird.
I think that's mostly correct, and at beginner/intermediate levels of play can very much be true. Back when I used to play, I'd often run into people who specialized in weird gambits like the Grob or the Latvian, because even though those probably won't win many masters levels games, they're full of traps which can trip up lesser players.
But even in mid-game, it might mean that if you know that your opponent prefers open / tactical positions, for example, you try to force a closed position, even if it may be slightly suboptimal.