Ruling out lung cancer already is a DARN good start. My Mom "presented" with non-small-cell lung cancer at Stage 4 (tumors that had spread to other organs) this past June and died within 3 months. No little spot in her liver, either: the size of a softball. Very, very aggressive tumor in an essentially inoperable place in her lung, as well, where it all started. Ruling out lung cancer is a good thing. A very good thing.
I do not know enough (other than to refuse to speculate wildly) about how many non-malignant and non-dangerous things can cause spots in diagnostic imaging, but you are definitely on the right track in heading for the people who do. While they are learning what is going on, your web medical IQ will go way up as you start to learn how to understand what they are doing, where they are heading, and what questions to ask them to help guide you both in the most beneficial direction.
I have been where you are, and did not get any good news at all. You are in my thoughts, and I wish you and your Mom the very best.
Unfortunately, always remember that it is called the "Practice of Medicine" for many reasons. You will be doing your homework to be the most informed patient advocate for your Mom that you can be, and that will help you both get the best care you can. Ask for and use any technical vocabulary they can give you, as it will help you in your search for answers, treatments, and hope.