Interesting - can lightening forks go as far as several miles from the main strike? Is that what you had in your yard?
I heard lightning goes from the ground up. The one seemingly in my yard is the first frame.
It’s an artefact from the light reflecting off the digital sensor, off the back of the lens then back to the sensor. The artefact matches the bottom of the “true” lightening bolt image. This happens on very bright scenes.