How so?

Spam, for decades, has been a matter of just shoveling truckloads of emails out the door and hoping that one or two get a gullible match.

Blocking spam, for decades, has been a matter of heuristic pattern-matching.

I don't see how that is the same as "fighting LLMs with LLMs", or how it could be said to be the same as how spam is made and used.