The scripture does not say God GAVE him a soul, nor does God say that it is immortal. Before I go any further with this I would like to make sure that the significance of this simple exposition of scripture is not missed. There is a world of difference between being something and having something. For example you can BE a carrot, or, HAVE a carrot. Are you getting the picture.
Lets go on.
If we look at the equation we can see that it takes two things to make a soul. This dust is referring to mans Physical body. If we look at our bodies we can see that it is made up of many different kinds of minerals, and organic compounds. After God formed us he then gave us the breath of life. At this point we are a soul, as defined in the Bible.