Atelectasis is the term where part of the lung fails to expand. As the phrase is liner sub- segmental this sounds like a very small area affected. Parenchymal scarring is where inflammation or infection has caused some damage to the normal lung tissue which has healed thicker than before (bit like a scratch on the skin leaving a scar)
However the overall comments mean that there is nothing on there to cause any concern.
Did you have some lung problems?
Its not something that I would directly relate to your surgery. I would have to see the CT to the location of the scarring. It could be as a result of previous infection, occupational exposure to dust or even heavy smoking.
The other test you might want to request is a ventilation/perfusion scan as this can identify pulmonary embolism which is a source of chest pain that may not be seen in CT.