I’m not a meteorologist, but I do know a thing or two about plasma.

Plasma is very short lived. Think on the order of microseconds at atmospheric pressures. So unless there was a massive linear source of power along the whole length, this isn’t plasma.

The visual effects probably have to do with the fact that the sun was very low. I’m guessing the particle size distribution in that line is notably different from the size of particles in the clouds surrounding it, leading to much stronger reflection of evening light.

I am curious as to the meteoroligical explanation for the line though.