It is a build - it's intend to be a final build and not a beta which may see multiple other builds. Ans all companies release their GM to developers (not just Apple) - they need to test them with things. The terms are not to be used interchangeably. They represent opposite ends of a scale.
1) If this were a textbook or technical article on the subject, and not an internet forum, then I'd agree with your pedantry. It's not, it doesn't alter your understanding of his post… so I don't.
2) Not all companies release their code to 3rd-party developers to test. Will Amazon for the Kindle Fire? I don't think so.
3) Even though many do release their RTM to developers I don't know of any outside of Apple that internally call them Golden Master, a coinage from Gold Master. If we're going to be overly strict shouldn't we stop calling any and all RTMs GM?