No 1 Why when they are not connected to the earth by any means does the Electricity arc into them.... and
No 2 does that happen to a Bird (of any sort) when they land on similar wires?
Even though they are not connected to the earth, the helicopter and the people in it have a certain electric capacity. It gets charged to the same electric potential when connected to the high voltage line (and discharged, and charged again etc, the line is AC).
The arc is essentially the same thing that you feel when you touch a metal object after getting out of a car, except that the charging is caused by friction in that case.
Birds do get the "same" effect, but their electric capacity is much smaller than that of a helicopter, so there is much less current and less (no) arcing.
Truly a spectacular job. I'm guessing they use the 500 because of it's size. Don't even want to think about what happens if anything goes wrong though...