Sure it's a blurry line but some formats are better than others for some specific tasks. JSON isn't the right tool for every job but it's a good enough lowest common denominator for data sharing.
I wouldn't want to use if for config files or passing complex data but then it's not designed for that.
TOML also has more "normal" notations for dicts and lists that are almost the same as JSON.
There is a distinction between markup languages e object notation languages. XML, HTML and Markdown are markup, JSON, YAML, TOML and most other are object notations.
(here my distinction, in general, is if they allow unquoted text)
I wouldn't want to use if for config files or passing complex data but then it's not designed for that.