Note: as anyone with an understanding of electricity can attest, "electrostatically neutral" is a fiction. In the current context, what Murtaugh would have said, had there been room for the full wall of text, is "The difference in charge between this layer and the next one down is much less than the difference in charge between that layer and the one below it. Also there is a very large body of air between us and the shear layers below, and the length of the ionized path up to us will be far greater than the path between those two layers. This weapon pulses, rather than firing continuously, and the beam length is less than half the distance between us and the next layer down, further ensuring that the discharge will occur below us, and will not extend back up here."
It should also be noted that the distance between Murtaugh and the shear layers is almost as great as the depth of Earth's breathable atmosphere, and far greater than the usual distance of travel for lightning in planetary environments.
But please do not for one moment think that this sort of behavior -- firing pulsed plasma weapons into giant thunderstorms -- is something you should be trying at home.