I am expected to serve clients in a lot of different domains.
When we were doing data science work for an insurance client, I stayed up late for weeks reading about actuarial models and how things currently work as well as learning all the jargon there is in the industry. I could probably pass the highest level actuarial exams at this point (or at least not fail too embarrassingly) [edit: OK I probably couldn't do this, but I could probably pass any/all exams related to the quant side] and also innovate superior premium pricing models using "Machine Learning". Not because I want to become an actuary but that's what's required to do good work.
When I worked in pharma, I learnt from other PhD's/PostDoc's on my team about oncology, a very specific type of oncology in fact, and everything that goes into Pharma companies and their marketing efforts, how doctors operate and behave. Not only that, but I learnt from an industry expert on all the nuances and subtleties that involve analyzing various types of medical claims data. (Hint: It's a total CF)
I could go on and on about the different domains I've had to work in. But the whole point is, being a generalist, in the sense of a dabbler, is utter nonsense. If you want to be a data scientist, you have to be flexible enough to work in any domain, and also have the gumption to become a specialist in the field, do something new in that domain with your shiny "machine learning" knowledge, while making sure your models are not GIGO from spurious statistical assumptions, and making sure you know how to code decently enough that your algorithms/code doesn't shit itself. This probably aligns closer to what the article was actually talking about..
(Edit: Sorry for the confusion, in my world the word generalist has a totally different meaning..)