In Chess, you can learn techniques used by players a few hundred points above your rating, but still make game-losing blunders (hanging a piece totally undefended, not knowing how to finish a winning endgame) that are easy to spot (if you are careful). Patiently eliminating blunders will do much more for your rating than learning myriad openings variations and complex combination moves.
In FPS, aiming moving and ducking are like learning how to move the pieces in chess. And sure, those are the basics to even play.
But when people talk about "fundamentals" they are talking about the emergent things that come from those skills and are usually unique to the game. In chess, this is stuff like don't hang your pieces, tactics like spotting skewers or forks, understanding endgames, and later general strategic goals like controlling the center or develop your pieces to "good" squares.
In FPS games, this often deals with understanding the flow of a map (choke points vs open areas, cover and sniper locations), proper navigation (efficient pathing!), role synergy, and how a match develops (at about 30 seconds I should expect an opponent, if they went straight path A, to show up around this corner).
MOBA games moving and attacking and using a skill are the language. Fundamentals involve map awareness, ganking, vision control, wave management, etc.
Fighting games move, jump, attack, block is the language. Understanding zone control, the Rock-Paper-Scissors of strike/block/grapple, how to manage your health and special meters, character movesets/matchups are the fundamentals. Picking character X against player Y is the meta.
Once you have all of that squared away, you can start doing "meta." That is figuring out optimal picks vs particularly optimal setups, researching your opponent to build a specific toolkit against them, etc.
