so a Japanese man jumps infront of a train and the train conductor and passagers all say the word じんしん, so I suppose it's 人身, which means human body and not suicide so I'm confused here.
人身事故 is a term which probably technically refers to any accident involving an injury, but in actual use it almost always euphemistically means "fatal" accident.
Whether it was an accident or a suicide doesn't matter at the time, the incident is 人身事故 until investigation reveals whether it was 事故死 or 自殺 or 他殺.