It's an odd concept by just the traditional definition of the term; being copied and redistributed (regardless of attribution) en mass is just the way that meme

It's an odd concept by just the traditional definition of the term; being copied and redistributed (regardless of attribution) en mass is just the way that memes propagate to begin with. Zooming in on both the twitter use case, and how most users of those platforms see meme ~= funny image or OC, a stolen meme is more akin to stealing a joke. So "stolen memes" is a phrase that makes zero sense for the broader definition of the word meme, but makes complete sense for the more specific definition.