Simple explanation, the higher the bitrate, the more data is dedicated to each frame to be displayed, so the higher the quality of each frame assuming the same resolution. This means fewer artifacts/less blocking, less color banding, etc.
Lower bitrate is the opposite, basically. The video is more compressed, and in the process it throws out as much information as possible while trying to maintain acceptable quality. The lower the bitrate, the more information is thrown out for the sake of a smaller filesize.
Resolution is the biggest factor that affects picture quality at the same bitrate. A 1080p video has a quarter of the resolution of a 2160p video, so it takes much less data to maintain a high quality picture.
You’re not wrong, but that’s also just a persona he plays, the hair and mustache are both fake. I don’t know how close the persona is to the real person, but I’m sure he’s hamming it up to some extent, just not enough to be a good person pretending.