Learning Haskell is like learning Latin, sure you'll gain deeper insights into other languages and language itself, but you aren't going to be able to do much by just speaking Latin.
Saying it is very inconsiderate of the efforts of everyone writing real world Haskell software.
Facebook uses Haskell, Github uses Haskell, etc... the metaphor doesn't hold and means this is just FUD.
On top of that, you're actually talking to a working professional Haskell programmer whose company depends on it.
What do you use Haskell for?
Sometimes background services.
Separating "I like and use Haskell" from "Learning Haskell will amplify your career and employability" is, I think, what they're going for, and I would generally agree with. "The exception that proves the rule" is a thing, after all.