> It likely is a collaborative filtering method. You get served what people "similar to you" have watched most. Similarity is based on your watching behavior. If you watched 1,2,5,6,7 and someone else 1,2,6,7,8. You will be recommended 8 as well.

Yeah, similarity of “preference” is approximated, in any recommender system, by this or some similar analysis of behavior with respect to content.