I really enjoyed that SO thread, and your answer. In my opinion your take is correct, to the extent that it is fascinating that it is a controversial topic. The majority of people, (and by people, likely limited to software developers), seem to not fully understand HTTP status codes. This is of course fine, the fascinating part is the extent they insist they do. Whenever the majority, in any technically field, opine something different, I assume they are right, and I've missed something. But having designed APIs for years, I can safely say that it doesn't apply here.
Also, the OP article does explain well what could cause this misunderstanding. HTTP resource nouns shouldn't ever be "guessed". The resource either exist or it doesn't. And if it exists, it either has a data, or it doesn't.
404: it doesn't exist
204: it exists and has no data to parse.
