Meh, it only happened to fork Elm to bootstrap early development and had no plans to carry on with Elm’s development nor trajectory. People in these comments are already confused.
The only interesting thing about Gren on HN is HN’s interest in Elm drama. I bet nobody here even mentions the language specifics but just meta discussion.
It usually isn't the best way to introduce it, but if you value clear communication it makes sense to say that it is a fork of Elm if someone wonders whether or not it is one. Otherwise you're venturing into territory where the meaning of words is arbitrary and only your favorite words to describe something are valid.
That would be throwing out the meaning of the word "fork" similarly but in a different way to denying how Gren started as a fork and thus is still one (though it's not the best way to quickly introduce Gren to its intended audience as a whole). There aren't simple algorithms to determine these things. It's the sort of job an LLM would be good for.
The only interesting thing about Gren on HN is HN’s interest in Elm drama. I bet nobody here even mentions the language specifics but just meta discussion.