Double encryption ??

[Oliver Hankeln]

Hello,

a friend of mine and me were just starting using GPG.
He encrypted a text for me an sent it to me. I was able to decrypt it.
BUT: He was also able to decrypt the encrypted message with his own 
secret key.
The only reason why this could happen as seen by us is that the text has 
been encrypted twice  - with my and with his public key.
We just want to be sure we didnīt make any mistakes. Is our assumption 
right?

Thanks,
Oliver