I suppose I’d say your relative is technically correct about the literary novels being presented, but the promotion is better off including both fiction and non-fiction than making sure the sign describes multiple types of books precisely.
Like geewhiz says, too, there is such a thing as collections of fiction which were written piecemeal and addressed to someone. Unlikely to be in this group of books, though.
I think you saw this on @tomchick’s shelf and commented. @Thraeg too I think. So I had the recommendation floating around in my head and picked up a copy recently. Great read. Now reading Out of Africa, Karen Blixen having been a contemporary, also very interesting.
Then I fired up MSFS and explored the Ngong hills :) Amazing country.