Yes. In particular a 'lightweight' variant, cf. https://en.wikipedia.org/wiki/Lightweight_markup_language

This wikipedia page includes reference to WhatsApp... Should it?

I understand that you can use bold, italic, underline, but that is where the comparison ends - the answer to Features is "No" in the comparison table versus others. Not all other comparisons include it.

It's almost as if someone shoe-horned it in for greater visibility. "Hey look at our app, it's better than competitors because it's listed here!" Yet it's competitors offer the same or more.

No, it is specifically markup which tries to be nice to read even unrendered. Reading HTML source code is rarely nice and that is also a form of markup language.