As you probably know, no test is 100% foolproof.
The main purpose of a stress test is to check for an evidence of blocked arteries. Blocked arteries are the cause of an angina pain, and result in an ischemic disease. Your stress test was normal.
Stress test usually reveals arrhythmias and any ECG changes (from baseline ECGs). It also detects coronary artery disease. It will reveal coronary arterial problems that are not apparent when a person is at rest (which is when most ECGs are done). It would not be very helpful in detecting fixed stenosis with collateral blood flow, or a low grade (= less than 50%) stenosis.
Because of the false positives and false negatives, another diagnostic test, such as an echocardiogram, is usually recommended in conjunction with the stress test. As you know, sometimes the false negative result can mean the presence of CAD even if the stress test findings do not support this. Because you passed the test with flying colors, the chances are you are in the clear and have nothing to worry about. This test should be repeated periodically, the frequency depending on your cardiovascular risks.
P.S. Do your heart and cardiovascular system a HUGE favor and quit smoking. It can be done!