Not that different from Android apps or Windows apps. Facebook also refers to them as apps so calling them "Facebook apps" is a pretty accurate description.
I'm not saying it's inaccurate. I'm saying it's ambiguous. Literally every search result I got on the first page for "Facebook app" was about a mobile app written by Facebook to access a Facebook-owned service (fb, WhatsApp, Instagram).
Since some people might not read the article and just the title, it seemed worth calling out.
Edit: ah, the title was edited from "Facebook app" to "third party social network app". So never mind :)
