Primal Urges - S2-E2
Character mistake: The radiation on the planet's surface is a problem, and the exposure between the shuttle and the entrance to the underground caverns is specifically highlighted as the main risk. And yet when landing the shuttle, they land facing towards the entrance with the ramp behind them, making the exposure time much longer than it has to be.
Continuity mistake: As Seth MacFarlane tells the crew to take things seriously, he's got his hands held parallel to each other. The shot changes and his fingers are interlocked.
Primal Urges - S2-E2
Character mistake: Isaac makes a statement regarding Earth's sun becoming a red supergiant. However, Earth's sun is not large enough to form a red supergiant, it will just become a red giant. This is something Isaac would know and not get wrong.
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