The best way to see if there is a nonrestrictive clause is by taking out the information between the two commas. If the sentence still makes sense, it is nonrestrictive.
Mrs. Smith, who’s son attends my school, is my favorite teacher.
If we remove what’s in between the commas, it’ll say Mrs. Smith is my favorite teacher. This is the correct answer.
The cottage statement seems more picturesque than the other.
People say UFO landings on Earth really happened, but I just don’t know. Have you ever actually SEEN one? I can’t find anyone who has. People say aliens landed on earth in the 1950’s, but come on, where’s the evidence? We have no recordings of the landings, no new technology they brought with them, and no new languages. I can’t imagine scientists wouldn’t have found a way to leak some kind of evidence after all this time. This is the kind of stuff they live for. I just don’t see how UFOs can really have come to Earth.