The longstanding meaning of the verb to slay is clear and chilling: to kill, murder, destroy.
There could be positive connotation - particularly in religious discourse (see the Old Testament etc) - but this has narrowed to describing the mythical: Buffy the Vampire Slayer, for example - but only in very specific circumstances like a just war. Even then it might seem tasteless to celebrate - Nazi slayer would be beyond the pale for many.
In contrast the Generation X use of slay is entirely metaphorical. To say you 'slayed an interview' is means to perform impressively. No corpses or physical battles are required, nor when you 'smash' or 'kill an exam. Think more in terms of punching the air because you've climbed to the top of the leader board on a favourite game.
Another distinction is that the new meaning of slay is no longer restricted to verb use: a party can be slay for example