It's irrelevant, unless you're proposing a technology dichotomy
Aliens have traveled all the way to Earth, but the only way they have to examine the planet from a distance is optics? Ignoring the fact that they'd at least have the technology for thermal imagery (detecting fires, lanterns, even people and animals, by their heat emissions), they could easily have uber-cool Star Trek grade "biosigns" detection.
Which means it doesn't matter at all what the surface looks like, day or night.
However, just for fun...
Year 1,000 CE, Daytime
With rare exception, the surface of the Earth would look like pristine, unadulterated habitat. The aliens would look down on a planet 99.99% free of all pollution (not including forest fires). They would see deserts, forests, glaciers, islands, lakes... and not a single electric light or asphalted road.
The rare exceptions are the handful of cities with 100,000+ populations. There were certainly a few, but very, very, few. Some thing Kaifeng, China; Baghdad, Iraq; and/or Cordoba, Spain could fit into that category.
Cities of this size would look a little patch-work, like looking down on cultivated land from the top of a mountain. But to be honest (and now that I think about it), the patchwork of farms would likely be much more visible than the crisscross of dirt or early cobble roads (and a handful of Roman concrete roads).
Frankly, I believe in the year 1,000 that the Earth would look barely inhabited at all — assuming all you have to look with is a telescope.
Year 1,000 CE, Night time
But, no electric lights. That means the much less powerful, much less likely to be on-all-night, and much more sparse use of lanterns and fires. Rather than the bright, almost pixelated look of a modern city at night, the aliens would see, maybe, a half-dozen or dozen areas where there was a soft orange glow (if even that, from space).
I wouldn't be surprised if your aliens saw anything other than black, with the possible exception of lightning strikes and active volcanoes.
Again, assuming all they have to look with is a telescope.
But it's inconceivable that the only thing they have to work with is a telescope. They can cross intragalactic distances — but optics are all they have to work with. Even if the only thing they have to work with is broad-spectrum electromagnetic radiation (which includes thermal), the odds are in my favor that they could count the hair on a woman's head from high orbit.
I don't believe your aliens would have trouble evaluating the Earth at all. If anything, without all those pesky humans gobbling up all the resources, the Earth in year 1,000 CE would look pretty plum.