IMO, the content can often be unrelated to science, as many tweets even by established scientists are about politics or other topics. There is also a large contingent of early career scientists trying to use twitter to get their name out there. Having a strong twitter presence can help assistant professors when to comes time for their tenure review, as peer name recognition does play a part in the decision (but there are other, better, non-Twitter ways to do this, too).

I assume he means it's made up entirely of armchair scientists. From what I've seen it's a lot of 12 year olds reposing mother jones or Vox articles who think they've discovered the solution to climate change. Science communities tend to be a lot more political and tend to attract more kids in my experience

Imagine a bunch of professors trying to be “influencers” instead of real scientists and you’ll not be far off.