Wider sentence spacing certainly predates the typewriter, but the question then was not "how many spaces" but "how much space". Someone writing by hand obvious

Wider sentence spacing certainly predates the typewriter, but the question then was not "how many spaces" but "how much space". Someone writing by hand obviously does not count a discrete number of spaces, and a cold-metal typesetter has a wide variety of spaces available: they might use a one-and-a-half-en space (either a single piece of type or an en space followed by a half-en space) or an em space. It must have been the introduction of the typewriter that brought the idea of "two spaces" instead of "wider space".