Not proven to have been caused by lightning, but a reasonable assumption; the effects are a bit more dramatic (and less beautiful) than the Lichtenberg figures. I'm puzzled by the comment at the link re the lightning passing from the front legs to the back legs; how would they know that? (Credit here)
Addendum: did some more searching and found this -
When lightning hits the ground, current flows through the earth in a wide area around the point of impact. This is how a lightning strike can kill a field full of cows - the long wheelbase of the average cow means that a nearby strike induces a significant potential difference across the ground spanned by the cow's front and back legs; current flows through cow, cow dies.Apparently that's why it's recommended that humans caught in the open should not only crouch low, but keep their feet close together - if you're not struck directly, you don't want your feet far enough apart to create a potential difference for voltage moving through the ground. First time I've understood that.