Continuity mistake: While in the shuttle bay, Dr Finn and her family are preparing shuttle ECV-197-2. During the rest of the show they are flying shuttle ECV-197-1. (00:01:15 - 00:05:20)
Continuity mistake: During the cold opening scene, Claire's right hand is alternately clasping Ty's left arm or lying flat on the bed as the camera shots change.
Continuity mistake: When Dr. Finn takes the covers off her son, Marcus, the white sheet is still around his legs. It's gone in the next shot, but back on his legs when she kisses him.
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