Essentially: You deleted your low quality config. However the config is actually a script that runs when the game starts, NOT a settings file. When the config is deleted, the game stops running it, but any settings it baked in are preserved until overwritten. Most low quality configs change settings that aren't touched usually, so they're never overwritten. Even maxing the game using the ingame video options won't fully restore it. Like others have said, either use a high quality config, open the old config and reverse its settings to the defaults manually, or tamper with your actual settings files to remove anything that seems abnormal, at which point they'll be restored to the default.