Sometimes you get some videos in the recommended list that don't even match with the content you usually watch, some reasons that shouldn't be taken on consideration of course are :
1-The Video's length: because videos that I noticed, some are long and some are only a few seconds.
2- Video's Category: as I said, the videos don't match with the content you're watching.
3- Video's region: I keep getting videos recommended from different regions.
So what do you think that youtube uses to recommend videos to people, based on what standards