Scott,
See the first few pages of CBM's chapter, "Inception of Ideal Golf Links." Doesn't give the specific reference, but it helps explain the timing and his thinking/action on the topic.
Niall,
As Tom mentioned, your definition of architecture was quite a bit broader than CBM's. Also, it helps to look at his comments in context. For example, part of his discussion is in the context of whether or not "golf architects" should have been considered professionals. In his mind, the discipline had developed to the point that it ought to have been considered a separate art, not necessarily linked to profiting off of golfing skill.
Regarding your "guess" that it wasn't CBM who coined the term "golf architect," that may be. But CBM said he wasn't aware of any previous references, and neither am I. Are you aware of any earlier references? Seems a better avenue to pursue than just guessing.