I find all this public key and private key concept is confusing to general people. A private key is an actual key that you can use to unlock an encrypted message. A public key is actually a lock that you gave someone so that he can use to encrypt message and only you can open it.

I believe some people, myself included initially, misinterpreted the "encrypted with" key as being the sender's key rather than the recipient's.

We don't know who that key belongs to for sure, of course, but it could be Snowden's.