Genetics play a role in the development of COPD.  It is more common among relatives of those with COPD who smoke than unrelated smokers.  Currently, the only clearly inherited risk factor is alpha 1-antitrypsin deficiency (AAT).  This risk is particularly high if someone deficient in alpha 1-antitrypsin also smokes.  It is responsible for about 1–5% of cases   and the condition is present in about three to four in 10,000 people.  Other genetic factors are being investigated,  of which many are likely. 
Noninferiority trials have serious inherent limitations , the main one being that (unlike in a superiority trial), given a finding of noninferiority, it is impossible to distinguish between true equivalence and poor execution or faulty pretrial a priori assumptions regarding expectations of benefit and event rates. In this particular trial, a 15% absolute difference in the primary outcome was arguably too large to use as a noninferiority threshold. That threshold implies acceptance of 1 additional COPD exacerbation for each 7 patients treated. If a superiority trial showed a week's extra steroids prevented 1 COPD exacerbation for 10 or even 20 patients treated (, a 5-10% noninferiority margin), I think many doctors and patients would endorse longer-course prednisone. This trial (as designed) would fail to detect that.