
Other mistake: Right at the start, as they're crashing, the computer narrates their rapidly-dropping altitude in feet. But the "altitude" dial we're shown is in metres. Most noticeable as they cross the 3,000 mark, when the computer voice and the height say/show the same number at the same time, despite the different units. 3,000m would be more like 9,000 feet, or 3,000 feet would be more like 1,000m. (00:03:20)
Answer: The book "Flatland", which is mentioned in the show, is a real book that may answer your questions in full (it's the story of a 3-D being experiencing the 2-D world and the 1-D world). In the 2-D world, there is no height, so there's no way to slice anything in half (horizontally). A being living in the 2-D world sees any object or being as a line (it's messy, but the lines have thickness, just not height, but all thickness is the same). So if the Orville was seen, it would only be seen 2 dimensionally and be seen as a line and others beings could just move out of the way. While there were buildings in "Flatland", perhaps this world doesn't have any, or the Orville didn't bump into any. There is death in "Flatland" when a being isn't careful and is poked, but these are usually by lines and triangles and the Orville would more like the circles and not in danger of poking anything.
Bishop73