The problem here is that if you use ``` as a token in a non-markdown language, then it's going to be very hard to embed that code in a markdown code block. That problem doesn't happen with other syntax as it's already escaped by the code block. `---` inside a markdown code block will render as a literal `---`.

Yeap, along with `+++`, `**` and mixing if I remember correctly. I don't understand the logic of using an non-standard syntax because some non-standard implementations may not render correctly.

Actually, yes, now you know for a fact that none of the Markdown implementation will render it correctly.

So, I guess, they used `~~~` instead and it was an error in OP post.