Well, duh.
Speaking as a working novelist (who has been earning a living that way for the past 19 years, thank you very much) I note that the editor quoted above was speaking of print sales, not sales including ebooks. A really prominent feature of the publishing landscape in the past decade has been the collapse of the mass market distribution channel -- small C-format paperbacks which are sold on 90 day credit: when payment is due the distributor must be paid in full or receive proof of destruction in the form of stripped covers. (This channel was originally created for periodicals and expanded to books in the wake of the depression and the second world war. Trade books sometimes come in C-format -- especially in countries like the UK where the mass market channel crashed and burned in the 1990s -- but usually come in hardcover and A-format or B-format: larger paperbacks. These books are returned intact to the distributor for credit, and a lot of bookstores rotate their stock on a 90 day basis, relying on the wholesaler's line of credit to cover their expenses.)
Anyway: mass market paperback sales in the midlist (not the bestsellers: the other 90% of the trade) fell off a cliff once ebooks showed up. Ebooks were about 1% of my sales in 2005, rose to about 5% by 2008, then took off like a rocket: I'm now with a publisher who prioritises ebooks (but issues hardcovers as well), with roughly 50-60% electronic sales. In contrast, the figures for my mass market paperback releases dropped from roughly 60,000 for my first novel, to under 10,000 a decade late ... although I'm earning about five times as much.
I have two hypotheses to explain this:
1. MMPBs were traditionally bought as disposable reading: the vast majority of customers wanted a cheap read, and binned/donated/re-sold their MMPBs on the second hand market after one read. (Hardcovers, in contrast, tend to be collected by fans.) Ebooks fill the disposable reading niche even better than MMPBs insofar as they're infinitely more portable, and these days you don't need a specialized gadget to read them: any modern smartphone will do.
(It's no coincidence that my rising ebook revenue took up the slack from my descending mass market paperback revenue.)
2. Amazon, the 500kg gorilla in the ebook field, doesn't release any figures for direct sales of self-published ebooks, but I'm guessing they're huge. A lot of writers bypass the traditional publishers completely and go direct to ebook via Amazon, who don't offer the range of support services of a Big Five outfit but who also pass more of the money through to the author. (Disclaimer: I'm with two Big Five publishers. The higher royalties would be nice but I don't like having to recruit and pay my own editors and proofreaders and typesetter, and I want to spend my time writing rather than being a one-man publishing business. There's this thing called division of labour ...) Anyway: about 90% of the self-published material (my opinion is based on a three year deep dive into Kindle Unlimited) is rubbish that, frankly, isn't ready for publication ... another 9% is decent commercial-grade fiction, and 1% is stand-out star quality stuff, and some of that is going bestseller under the radar. That is: because it's sold on Amazon and AMZN doesn't feed numbers to Bookscan AIUI (Bookscan captures retail sales at the EPOS terminal) they don't show up in the charts, even if they sell a million copies. And these books are invisibly eating away at the major publishers' market, corroding it below the waterline.