The title of the article makes it seem like it's some mysterious, unknown rocket that could have come from anywhere, but in fact (as the body of the article adm

The title of the article makes it seem like it's some mysterious, unknown rocket that could have come from anywhere, but in fact (as the body of the article admits) there's just some uncertainty as to which of two specific missions it comes from; it was initially thought to be from a SpaceX launch, but further analysis indicated that it was probably a Chinese launch. China denies this and says that the rocket stage from that launch re-entered and burned up, so that's pretty much the mystery.