Why is this person shocked?
They are shocked because the resistance of the ground for the distance between their feet is higher than (or comparable to) the resistance through their body. The earth does have high resistance, but there is also a few thousand volts there.

This is the same reason that cows and sheep are more likely to be killed by a lightning strike if they are standing perpendicular to the ground current flow.

If you're ever in a lightning storm in an open field or in the situation depicted above, just stand with your feet very close together. It might save your life.