Because it happened out of the blue, I'd assume you were not able too see if the tach dropped to zero befor car shut down.

If you happen to see that happen while driving then its a crank position sensor issue.

That sensor will tell the computer along with the cam sensor and others to keep giving the car fuel because its still saying the motor is spining. Once that connection is broken, as in a faulty CPS, it will cut fuel to the injectors and shut the car off.