[I spent about 30 minutes trying to nuke my drive. I did the cat-on-head trick. I walked around in socks. I walked around in wool socks. I tried to moonwalk in wool socks on a faux Persian rug.]
Did you tried to charge you by holding the HD in your hands? (Then there was not differential potential between you and the disk).
If before touching the HD circuit, you touched other part of the disk, or object touching the disk, then most probably you grounded the disk at the same potential than you.
You should also had tried to ground the disk as it is grounded when is screwed and connected to the power source.
Anyway, if air was too conductive, then you would be not allowed to make an enoug strong potential.
Hardware is not packed on costly antistatic bags because manufacturers like to throw away money.
Did you tried to charge you by holding the HD in your hands? (Then there was not differential potential between you and the disk).
If before touching the HD circuit, you touched other part of the disk, or object touching the disk, then most probably you grounded the disk at the same potential than you.
You should also had tried to ground the disk as it is grounded when is screwed and connected to the power source.
Anyway, if air was too conductive, then you would be not allowed to make an enoug strong potential.
Hardware is not packed on costly antistatic bags because manufacturers like to throw away money.