Well, it doesn't make the substance wrong. This paragraph rightly summarizes it:
"The fact that most programming languages don’t give enough semantic information for their compiler to do a good job doesn’t mean it necessary has to be so. Functional programmers just trust that their compiler will properly optimize their code."
The substance of the statements I quoted was wrong. As I wrote elsewhere, I do agree with the broad statement that the combination of functional and imperative features in OCaml works just fine. But if the semantic information you give to the OCaml compiler is "linked list", it will use a linked list rather than a data structure that might be better for the task at hand.
