At that height there should have been no induced voltage in a single strand of strait wire unless those transmission lines are running over voltage
There is a reason why high voltage wires are at that particular height
And discharging a cap with a screwdriver making a direct short is so stupid it is not funny
They are renown for exploding when you do that, he should have put a resistive load across it .
In any case he got enough electricity probably to power a reasonable LED lamp for a day or so
Usually all of these "free energy" ( stolen ) from overhead power wires are BS but that one seems fairly ligit
However it is more likely micro amps than milli amps