You're confusing "putting words in [your] mouth" with 'taking your reasoning to its logical conclusion'. As for the idea that because the BBC New Series Adventures has included audio books and anthologies they would consider releasing a novelization (which they have never done before period) let alone of an unreleased story, that's a truly herculean leap of logic. If that's what you're suggesting Harness made, again, you're suggesting Harness is incompetent.
So to reiterate, we now, to be incredibly charitable to you, have four options.
- Doctor Who photo novelisations - Assuredly not, the tone, subject matter, and level of literacy are in complete contradiction with this line of books.
- Target novelisations - Highly unlikely, if not outright absurd. They've never done an unfinished work, not even Shada, and for the New Series touch prominent stories within that season. If Harness were to pitch a story to Target it would most likely to be his Zygon two parter, to pitch this story is to know it will be rejected.
- BBC Books novelisations - Similar levels of likelihood. They haven't done any New Series work at all and in the relevant time period it seems to be entirely written by James Goss.
- BBC New Series Adventures - Utter lunacy. They don't do novelizations, this reading requires Harness to be using the terms of his trade wrong, and the line is all but dead creatively, as well as only putting out seven books since 2015. He'd be better off going to Obverse.
Since none of these four options, and again, I'm being immensely charitable to even consider four, is likely, we turn to the other alternative. It was a framing device. Reductio ad absurdum is evidence. It not being a framing device leads to absurdity.