No, chances are he didn't understand it because the sex depicted in LOTL is a bizarre, anatomical nightmare unrecognizable as any kind of sexual intercourse familiar to people who aren't totally up Morrissey's central zone.
I actually sort of agree with this, in that I'm also a bit puzzled by the fixation on the descriptions of sex. They're badly written and cringe-inducing, but so are many other parts of the book. They're not even anywhere near the worst thing about it. Furthermore, sex isn't an easy thing to depict well in writing, and Morrissey is not the only person to have written sex badly. He's no where close to being one of the worst offenders, either.
That said, "any expression he uses is a product of his craft" is a meaningless statement that makes no actual point. The words are a product of his craft.....and so what? A performance artist could take a shit in public for an art piece, but simply being "a product of their craft" doesn't make the result inherently good. Similarly, putting words together to form a sentence is not remarkable in and of itself, even when Morrissey is doing the writing. Of course he's free to realize his artistic vision in the way he sees fit, which extends to his word choice and phrasing, but unfettered expression is not necessarily a good or beneficial thing all of the time. It's also not exempt from criticism.