stage4 non small cell lung cancer

my x husband has been diagnoised with stage 4 lung cancer. he has a 2cm tumor in right lung that was biopsed and told it was cancer. left lung has suspicious leasions but cant biopsy. he is a smoker but he has no symptoms. he actualy had a mild heart attack and while in hospital for that they did chest xray which lead to finding the cancer. the doctors dont know for sure if the left lung field is cancer and also it has not spread any where else. my question is how can they classify this as a stage 4. he is 70 years old