Yes, our confessions do state that in both the Apology of the Augsburg Confession and the Solid Declaration in reference to Original Sin. That is correct. They are silent on the issue of Creation outside of our catechism which says simply that “I believe that God made me and all creatures”.
Both our confessions and the Scriptures are silent on other biologically compatible beings outside the Garden, and Lutherans have a habit of saying where the Scriptures are silent, we remain silent. Yet, there’s the evidence of science that seems to indicate there were others. What do we then do?
Our confessions speak of the image of God as “a wisdom and righteousness implanted in man that would grasp God and reflect him, that is, that man received gifts like the knowledge of God, fear of God, and trust in God.”
I think what you’re asking is more difficult to answer for those with a more literal reading of Genesis, but let’s say we take that perspective. Did those outside the Garden receive that implanted righteousness as well? This unique calling? If they didn’t, it’s not really an issue is it? They wouldn’t have capacity to lose it. But it all ultimately is more of an academic question, I think.