Sharing contact info without consent

Hey all,

I just recently got a number of a new person. Just first name. Their last name was never typed in my phone - contacts or messages. Today, in the messages thread, it is suggesting that I update their contact info with their last name (which I didn't know) and their photo (which was never shared with me). How did this happen? And is it sharing my last name and photo with this person?? How do I turn off this feature? It makes me feel very unsafe.