I wouldn't say the used an uncommon language. They build some kind of tool to run on top of Elm which wasn't inline with the goals of the Elm project (unlcear how). Seems like something that should've been investigated before commiting
It is inevitable that someone will use a language in the way the developers didn't intend, but this is the only time I've heard of the developers specifically setting out to break their language for some users.
that seems to be the angle presented by the author but that doesn't mean that is what happened
Elm author is quite vocal about wanting people to only be able to do things one way. It's the reason people choose Elm.
The Elm guy is infamous for this kind of thing
That's not functional programming at fault; that's a case of hostility toward users.