Is the hadith about not initiating greetings to non-muslims authentic? And what is its explanation?

> Abu Huraira reported Allah's Messenger (ﷺ) as saying: Do not greet the Jews and the Christians before they greet you and when you meet any one of them on the roads force him to go to the narrowest part of it. Is this an authentic Hadith? Can someone explain this to me, why did Prophet Muhammad (SAW) say this?