I thought non aggressive meant " non aggressive " so why would i see an article of a dr. telling his patient with non agg/lung cancer that he only had 6-18 months to live how is that non aggressive ?

I agree!: "aggressive" is a subjective, descriptive term almost arbitrarily used to define cancers; this term is never used by pathologists when codifying tumors. Many cancers have some features that would be considered aggressive and others that would not. Any cancer that could lead to someone's death in less than a year should not be described as "non-aggressive".

Terminology problem: The context in which the term non-aggressive used is relevant but your point is well taken as any cancer that results in an average survival of 6-18 months is not non-aggressive. Having said that there are patients with lung cancer with a shorter survival due to disease biology, stage of disease and patients' baseline health.

Terminology : Cancers are evaluated by a microscopic assessment of the cells. The cells can vary in their appearance based on a variety of features. If those features look "less aggressive" the cancer is called "low grade" and "well differentiated." even those cancer types can act badly if the cancer has a high metastatic proclivity (ie lung cancers).