NDJSON is a fork of https://jsonlines.org/, which has been around since 2013. I’m sure the concept is even older, but it can be helpful to have a name and a spec (no matter how small) for everyone to agree on.

Yes, but having a spec (however trivial) means I can tell someone to use "nd-json" and send them a link to the spec, without having to debate about escaping, utf-8, etc.