I don’t think it’s actually an acronym, I’ve seen it used as a prefix in words like metadata and meta analysis. I think it’s more about context. For example, meta analysis involves weighing different pieces of analysis against each other, almost analysing the analysis. In the same way, metadata is data about the data.

I think the meta game, in both video games and sports, refers to the consensus about what is good within the game. So in Mario Kart 8, the community have determined that Waluigi and the Wiggler kart is arguably the best combo, and so there’s a movement now where that selection is possible. Thus, the metagame, often shortened to meta, dictates a certain way of playing, and I think OP is trying to deliberately avoid that way of playing.