This weekend, an explosion from a homemade bomb shattered the peace of a mild Saturday evening on a quiet stretch of West 23rd Street in Manhattan’s Chelsea neighborhood. Within a few minutes of the 8:30 p.m. blast, local news apps were pushing breaking news of an I.E.D. detonation with scores injured, setting off a night of confusion, uncertainty, and fear (at least, for people outside of New York — more on that later). . .