static electricity from the high voltage line. It can happen if you are barely touching the metal. If you are making a firm contact with metal it will drain off static. I have been in high voltage for 45 years and that is not uncommon
If that were the case, the rider would also experience the same static charge, but it wouldn't be static charge anyway because the source of the electromagnetic field is AC. If it was a high voltage DC power line I could see this. I do agree with the fluorescent tube lighting up. The alternating e field excites electrons inside the tube and they give off their energy as light as they fall to lower energy levels. Also, if it was ESD it wouldn't feel like a constant shock, it would just pop you like when you wear wool socks across the carpet.
I don't know why the power lines are causing this or that they even are. It is interesting that it happens around EHV transmission lines. I'd have it checked out.