I think the writer means literary in the narrower sense of 'literary fiction'. Christie was a genre writer; like F/SF etc. I understand that wasn't quite respectable in the upper echelons of the book world. Certainly the reviewers in places like the TLS would be primarily interested in literary fiction.
The article may seem to take that view, but dispels it at the same time: "a list of 100 or so English woman novelists of the 20th century, a list running from Margaret Atwood to Virginia Woolf." Then it comes up with other possible explanations, all speculative. There's no conclusion.
Virgina Woolf wasn’t so highly regarded until mid century, well after her death. Before that, her reputation did not extend outside a circle of modernists. The Bloomsbury scene in general were countercultural even within the English literary-fiction world.
