[spyder]

It's likely an arcing powerline (see the reddit comments): https://www.reddit.com/r/videos/comments/1lrk1rz/incredible_...

[MisterTea]

Reading through the comments and reviewing the video does indeed point to arcing power lines. Ive seen videos of fast moving arcs across medium voltage lines that looked like a horizontal jacobs ladder. The lines over current protection equipment might not instantly trip as the current might be limited by enough impedance in the equipment. Disappointing reveal.

[JKCalhoun]

That sounds plausible.