I would guess that for a given class of videos, there's going to be a fairly regular amount of dislikes that are going to be because of behaviour like "I am not

I would guess that for a given class of videos, there's going to be a fairly regular amount of dislikes that are going to be because of behaviour like "I am not interested in this video". So if you come across a video in that class of videos (e.g., car repairs), and it has a much higher ratio of dislikes to likes, it's probably a good indication that there's more to those dislikes than just "I'm not interested" -- more likely the video is factually wrong, poor quality, etc.