The causal link to social media is presented very simply in the article, but I suspect that's mainly because the article is not about diagnosis, but about the prevalence of the pattern.

There is a lot of data to support the social media effect specifically (some referenced in the linked articles from Twenge), and I suspect the next few posts from Rausch will dive in more deeply, so it's not right to claim that they're jumping to convenient answers - these aren't casual bloggers sharing their reckons.

edit: actually there's a heap of related writing on that site, e.g. https://www.afterbabel.com/p/social-media-mental-illness-epi...