Next LS author here! I would love to hear about how your emacs experience went and what your setup/config is. My emacs skills are not the best (zero), so I've not been able to really work through any of the kinks.
I have recently gotten it working tho with vanilla emacs with eglot, as well as doom emacs (again, with eglot).
That's fine, but generally people on use that expression in a negative way, so I think it's reasonable to ask for explanation of why you think that.
In general I don't think it's fair to leave drive by comments like that without elaboration, as others might just see it and take it at face value when further clarification might reveal a misunderstanding.
The answer to your question is in the FAQ on the website for Next LS in particular, and a motivation for the whole elixir-tools family of projects on the home page
Literally read halfway down the article before they say that "working overnight" is also in the "probably carcinogenic" category and that the organization is known for publishing confusing results that cause panic.
I interpreted their message as saying Erlang is more functional than Elixir, which didn't really make sense to me personally. (I think they are both the same amount of "functional")
In this case, its an extension of the phrase but using the word built instead of made.
Ref: https://grammarphobia.com/blog/2017/02/scratch-made.html