It seems you're shifting the discourse here. In the context of LLMs, "to understand" is short for "to have a world model beyond the pure relations between words". In that sense, chess engines do "understand" chess, as they operate on a world model. You can even say that they don't understand anything but chess, which makes them extremely un-intelligent and definitely not capable of understanding as we mean it.

However, since an LLM is a generalist engine, if it understands chess there is no reason for it not to understand millions of other concepts and how they relate to each other. And this is the kind of understanding that humans do.