I'd liken it to accidentally getting a high ranking website on Google without thinking about it.

It doesn't mean you can't deliberately game the bot. It means you can analyze how and then replicate it (aka SEO).

If I can unintentionally sway the LLM agent, then I can figure out how and do it intentionally (aka GEO).

Either way, if you've used LLMs, then you it's trivially possible to sway them. That's the only proposition you need to accept for GEO to be possible. Though it's far worse than possible: I'm sure it's widespread and ubiquitous.