Origin from Clay — Adam or the Womb

I think it is simply referring to the origin of the human being — that we were made from organic matter, from clay, from the earth. I would not complicate it more than that.

There are other places in the Quran that mention the stages of development in the womb — the nutfah, the 'alaqah, the mudghah, and so on. Those passages are specifically addressing that developmental process. This passage is making a different and simpler point: our origin is this earth, this soil. We came from it and we return to it. The clay is not a reference to the stages of conception — it is the foundational material of the human being as Allah created our kind.

Adam (AS) was specifically made from clay, and we are descended from him. So "our origin is from clay" is true both in the sense of our first ancestor and in the sense that our bodies are built from the same organic matter that makes up the earth.