"ChatGPT and other LLMs don’t remember everything you say" in the title is contradicted by the "Reasons to worry anyway", because OpenAI does remember (store) everything I say in non-opted-out chat interface, and there's no guarantee that a future ChatGPT based on the next model won't "remember" it in some way.
In the sense of a chat bot that people are interacting with, it doesn't remember. That's an important distinction, regardless of what OpenAI does to save your interactions somewhere for whatever purposes they may have in mind.
The article reads as "no, but actually yes".