LOL - It should say "an electric arc occurs" It jumps from one conductive material to another. The insulating properties of the air can no longer stop it and it transfers to the other object.
I have always wanted to build a tesla coil... they look fun 😉
That was a crazy video. Your idea of fun is a hell of a lot different than mine.
Even when the nut job jumped, the electricity traveled from his feet to the ground.
That looks about as fun as hitting my thumb with a hammer.
Each to their own, and if you ever do build one of those death-defying contraptions, don't let the wife see you playing around with it.