According to the Elizabethan definition of the term, the first one ("Lightning strikes and kills a young man") is a tragedy.
The Elizabethan definition of "tragedy" underlines the idea that a tragedy always ends in disaster, which generally brings about the death of an important character. Moreover, there is always a fatal flaw that leads this character to his/her tragic end. In spite of this flaw, the audience generally feels empathy for the victim. All these features can be found in most Shakespeare's works, such as Macbeth and Hamlet.
The first option is a tragedy because it concludes with a man's death, which is the appropriate outcome of a tragedy according to the Elizabethan definition of the term. Moreover, his death is caused by a fatal occurrence (a lightning strike).