The HN title is misleading - it wasn’t a bug report but the Yubikey 4 replacement. The process by which it happened seems understandable: they used their existing store to process replacements (you got a coupon code for the same model as your old key) and notified all past customers when a major new standard shipped.

They should have handled that better and made it clearer under which conditions you’d get email but it’s way down the list of annoying corporate email practices.