I just got back from having my 11 year old son tested for allergies and it turns out he's highly allergic to many things and will have to have weekly injections. The allergist had sent us to get xrays of my sons lungs and sinuses and there are white spots on my sons lung xrays. The doc asked if we had lived in southern California or if we lived on a farm and when I told him no, we've lived here in Oklahoma all his life he said he'd have to have the radiologist look at the xrays. I came home and got on line and found this posting and was curious if you found anything else out or if anyone else had experienced such a thing.
White spots, as you have already guessed, can be caused by many things, including seeing blood vessels at a straight on angle. These can be calcifications, lymph nodes, vessels etc. If there is a question following routine x-rays, the CT scan is very appropriate and should lead to more definite answers and decisions.