The author could have done a better job of explaining this, if he would have said "Einsteinian Space" rather than "space" in that section. That's fairly easy to infer from the context, but it could have been explained better. Einstein viewed "space" as a vacuum. Tesla argues that view is flawed, that nothingness by definition can't have any properties, and as a result can't bend, because there's nothing to bend. He proposes aether/ether as an alternative explanation of "space".