We've just pushed a change to remove the source of confusion. That option is no longer relevant as we no longer show purchase information in feedback to 3rd parties, so we've replaced the option with a message indicating that your purchases are private on Etsy.
Purchases
Who can see your purchases?
[x] Everyone (public)
[ ]Only you (private, between you and the shop owner)
I then decided to opt out - a decision I only knew I had to make after reading the Ars article.