I believe in the cited article the author was simply pointing out to the fact that it is easy to learn the syntax and basic semantics of the language.
It is extremely hard to write high performance Haskell, same as it is hard to write high performance C. And additionally I think it is foolish to claim that "Haskell is no harder to learn than any languages". Definitely there are certain misconceptions (like you need to know category theory to learn Haskell) which needs to be debunked, but it is quite difficult to grasp the evaluation semantics of Haskell and pretending that it is easy and natural will simply shove more users away from the language.
It is extremely hard to write high performance Haskell, same as it is hard to write high performance C. And additionally I think it is foolish to claim that "Haskell is no harder to learn than any languages". Definitely there are certain misconceptions (like you need to know category theory to learn Haskell) which needs to be debunked, but it is quite difficult to grasp the evaluation semantics of Haskell and pretending that it is easy and natural will simply shove more users away from the language.