Movies I just watch was surrounded by the related video section today.
But in that were some porno movies within my related video that I haven't watched...
What is related video?
Answers: Related video are those videos next to similar tags. People close to to cheat the system by adding irrelevant tag (in your case, tag that you also had surrounded by your video) to get more view... that may be why there are porno video there. =/
Adding irrelevant tag just get people upset. I know I take frustrated with it. You can report the porn video.