The seed drill surely was one of the tools that made large urban populations sustainable, and was - together with other advances in agriculture - in a way providing the foundation for industrialization (although I can't say whether 10 is the correct factor). I don't know about any Roman versions of seed drills, though there were Chinese and Babylonian ones pretty early. These, however, have never made it to central/western Europe (which seems to be your main area of interest, if I read your question correctly).

"European" seed drills were only invented by mid-/late-16th century, so they can probably be considered more of an Early Modern invention than a Medieval one, as far as Europe is considered. Early Seed drills were, additionally, neither reliable nor economically feasible. From an mechanical stanpoint, they were only reliable from around 1700 on. And even then, seed drills were basically high-tech farming tools and not at all commonly used. They only came into common use in the mid-19th century, when they became affordable to average farmers.

So in a way, the author's claim is true, but it basically has nothing to do with the Middle Ages. Which is a general problem I have with this essay (I have just scanned it quickly, so I may have missed something): the author basically takes (military/demographic/agricultural/...) history from a span of about 1,500 years and tries to weave a coherent picture out of that. As far as I have seen, they calculate village sizes in dimensions you could hardly call Medieval (you would expect those kinds of numbers in the German-speaking part of Europe in the 16th century) and then calculate army size based on Roman armies, even though armies of similar dimensions were not again seen until well after the Middle Ages.

Of course, they are going for a writer's guide on how to build a medieval fantasy-world, so the readers' perception of the world as probable is much more important than historical accuracy anyway. And for that, the guide would probably work well. :-)