The incoming missiles had to have been close enough to represent a threat, ie their tracks pointing close towards USS Mason in order for them to release weapons x3 + decoys and likely ECM, over at We Are The Mighty one article has statements from USN people saying the incoming missiles weren't struck by the SM2/ESSMs, but the incoming missiles were defeated by other methods, ie ECM/decoys primarily and splashed before the USN missiles could intercept.
I wonder what the ROE are in the area, I would think they would be tracking the incoming missiles from their own radar systems on Mason, plus all the other ISR/sat assets the US has in the area, right from their launching point, and as AckAck said, why weren't there counter battery missions launched to stop any further potential threats/launches? Maybe there were and we just haven't heard about it, it would seem to be a pretty sound tactic to flatten the launch area/launchers to a: stop any more immediate potential launches, but also b: to take out those responsible, and remove some trained/experienced crew threats from the board as well.