it's a metaphor... isn't it?

I admire Geoff Pullum greatly. But the man has a bee in his bonnet about what he calls "linguification" (To linguify a claim about things in the world is to take that claim and construct from it an entirely different claim that makes reference to the words or other linguistic items used to talk about those things, and then use the latter claim in a context where the former would be appropriate.)

Today he writes:

Fred Inglis, emeritus professor of cultural studies at the University of Sheffield, reviews George Steiner's My Unwritten Books in this week's Times Higher Education (31 January 2008, 44-45), and describes Steiner's conceit (a survey of seven books that he claims he would have written had he the time) as "a memoir in the imperfect tense of the subjunctive mood."

...The linguistic claim is not true, and is not supposed to be believed. Inglis merely means that the book is a memoir concerning uncompleted works that Steiner hoped might be written. He expresses this in terms suggesting he is talking about verbal inflections for tense and mood, though in fact he is not. But why? Why a false claim about tense and mood to cloak a (possibly true) claim about nonlinguistic reality? Is Professor Inglis showing us that he knows how to brandish technical terms from traditional grammar, in the belief that this will convince us he is clever enough to be writing a review of George Steiner? I do not know. I have never been able to answer why-questions about linguification.

Why? It's a metaphor. Now, he always says (this protest from a post on saying "you can't say X without saying Y" or "People are now putting X and Y in the same sentence all the time"):

I'm not ignorant of the (irrelevant) existence of hyperbole or metaphor or synechdoche.

What I wanted to draw attention to was simply the strange practice of publishing linguified claims: for example, saying the name X is invariably followed by the phrase Y when it isn't, or saying X is always accompanied by the qualifier Y when it isn't, and so on and so on. Why linguify? I have no idea. It just doesn't look like a good writing idea to me.

What I don't get is why he insists the metaphor is "irrelevant" in these cases. Just because people are making their metaphor out of linguistic terminology doesn't make them invalid (the metaphors, that is). Metaphors are always untrue.

The memoir isn't, of course, written "in the imperfect tense of the subjunctive mood." I sincerely doubt that any person who read the sentence thought so, any more than people who say "use the past tense" to indicate that someone is dead, or more often that someone has accepted that someone is dead, mean than only the past tense is being used.

As far as I can see, it's just a common, garden-variety metaphor. And I completely fail to understand why Pullum insists that this one category of speech (referencing "the words or other linguistic items used to talk about those things") is so vastly different.

Maybe I'm just missing the boat (though there is no boat) on this.