No, Markdown is "syntax", quite literally not about structured data in any sense of the word, at least for existing pre-LLM developers where "structured data" has a real meaning already, you can't just go around redefining what concepts mean :)
> determine which parts of the text are code and which aren't
With this argument you'd could claim ASCII/plaintext is "structured data" too, just group code with "===" and that's evident. Obviously that doesn't make a format "structured data".
OK, this argument is getting semantic and, therefore, uninteresting. I think you know what I meant, even if I used some words in a different way than you would have liked.