I think the author of the post was referring to the fact that Belgium is a multinational state, comprised of Dutch-speaking Flanders and French-speaking Wallonia.
Lucky you! I tried learning with examples generated by ChatGPT and none of them worked at all. I then learned the basics of the API by reading this excellent tutorial: https://osm-queries.ldodds.com/tutorial/, and realised that, in hindsight, ChatGPT's answers weren't even close to being correct.