I started programming professionaly in 2005 and I can assure you that back then, outside of the browsers, people really didn't know or understand response codes.

There's a load of early, popular, Stack Overflow questions that revolve around what status to return when, and how to actually return those codes in your language. For example, in ASP.Net/IIS it was actually quite hard to stop IIS 6 (?) from swallowing your 500 xml response and serving a custom html error page. If I remember correctly some browsers didn't support PUT properly either.

So while you are technically correct, the codes were in use, you are historically wrong, few people outside of a small community understood their use.

I remember this article from the first time around, when people were really getting into REST and there was a fierce debate about strict REST Vs RESTful. In reality RESTful has mainly won and this article was on the wrong side of history.