As I recall from my school days, it takes 20,000 volts to jump 1 cm in dry air. It is hard to judge the gap there, but I would guess it is between 1 and 2 cm. That's enough to make you jump.
One of my instructors in the Navy electronics technician school liked to say, "It isn't the shock that kills you. It's the protruding objects on the far bulkhead."