That's odd. If you're using a shared computer/device, consider signing out of any Google services when not in use. It is possible that you're still signed in while someone else browsed through YouTube. If you notice anything else, let us know.
You can remove these videos from your watch history, here's how: https://goo.gl/TUcVFq . Also, consider changing your account password, which might help the occurrence. Hope it helps.