I think you got downvoted because you supplied a link and definition that involves a very specific situation that doesn't apply to the discussion very well. The discussion isn't about celestial bodies in our solar system, but celestial bodies around other star systems in a fictional universe. On top of that you're having a conversation in a non-professional, non-scientific forum where everyone will be using relaxed definitions about things commonly found and referred to in popular literature and games. Reading books, watching shows, and playing games we don't generally come to a screeching halt when "planets" are mentioned. You say "planet" and 99.9% of the time we all know what's being talked about. Similar to when a person asks for a kleenex we all know they technically meant a facial tissue. Someone mentions planet with the understanding that it could be technically an exoplanet, dwarf planet, or a collection of pixels. Saying "planet" is much easier than saying "a bunch of photons emitting from the display device that resembles an image of what could possibly be a planet, or moon, or exoplanet, or dwarf planet, or satellite, or...."