iPhone 6 contacts appearing that I don't know I have contacts appearing in my iPhone that I didn't put there and don't know. How is this happening?
Possibly you have a service enabled on your iPhone which adds another set of contacts. (It might be Facebook contacts or whatever else.) 

Check the Groups in Contacts and try switching the different groups off to see which one's adding the contacts you're seeing. Once you know which group is responsible for that, you can clean that up.