The word "gamist" currently has two different meanings in an rpg context. One derives from its use by the Forge in GNS theory, which was itself based on the
Threefold Model which dates at least as far back as 1997. This refers to challenge-oriented play ie challenging the players.
The second meaning is, in my opinion, much more recent and means something like a dissociated mechanic or
ludonarrative dissonance – a game mechanic that doesn’t refer to anything in the game world or is at odds with the 'reality' of the game world.