This is likely true for many companies. However, it is also a metric for what type of working environment it will be. I value being able to learn quickly and creativity over pre-training.
The article doesn't understand programmers. People will stay because they are passionate about OCaml and there are not a lot of OCaml jobs.
When hiring for a permanent position, I have the expectation that a programmer can learn a new language and environment. An OCaml programmer for a position that is python or C would be looked on very favorably. Far more attention-getting than “full-stack programmer”.