The phrase "to happen to" means that something occurs by chance or accident, without being planned. It is a passive voice construction where an action happens to someone or something rather than them actively doing it themselves.
But what happened to people just being respectful of one another. (religion.blogs.cnn.com)
Consider a general rule: if it would seem abnormal or unusual if happening to you, then it is likely abnormal or unusual in your pet. (okcpetsmagazine.com)
Our top pick just happens to also be our choice for best laser level for builders. (geekwrapped.com)