Do people know that "small" talk is a form of invasion of privacy?

Your use of the phrase 'small talk' is not correct here. The very definition of the phrase is that it's NOT intrusive. It's the small things in life that people don't care about sharing. Favorite movies, music, sports, hobbies and the weather can all be classified as small talk. Something as personal as 'Are you a virgin?' NOT small talk. And yes I do think those kinds of questions are rude and very uncomfortable. Most likely the person asking has some social issues.