Well, being that his view is theocentric, perhaps Augustine sees the human beings as God's helpers. Meaning that if it weren't for God the human being wouldn't have been present at all. So them being present in his life was more of an effort on God's part than it actually was for those who helped. Yes, it wouldnt hurt to give the helpers some acknowledgement for the roles they played, but to Augustine they were probably smaller parts to a greater plan the God orchestrated. Therefore, God actually would deserve the ultimate praise.