Was this rude in your opinion?

I've been married for 6 years and the other day I walked in and heard my husband speaking on the phone to his sister and before I could make it completely in the house I heard him saying that while he was gone somewhere friday morning that he left his cell phone recording to see what he could hear. He says that this was eves-dropping and was rude! If you walked in on your spouse saying he had recorded you would you stop to listen?? If so, do you think this was rude??