The linked study uses data from peasant farms in developing economies (Madagascar, India, etc.) from half a century ago or earlier. From the point of view of the west, that it would be measuring the productivity of very very small farms vs very small farms where the vast majority of labor is done by hand. Skimming over the article it seems that it concludes that under pre-mechanized conditions, larger farms have less available labor per unit land area. And that labor per unit land area is an important factor in agricultural productivity. This is hardly a surprise.

This is very much not like how farming is done in developed nations or even most developing nations today. And unless you want to force people to live like dirt poor peasants of the past, hopefully won't ever be done again.