so.. a Unix operating system that IBM developed specifically for the rs6000/pseries/power8 servers runs better than Linux. shocking.. even more shocking that the article is hosted on IBM's own site to tell us so.
obviously, AIX has existed longer than Linux, so it's code maturity is better.
Linux on the other hand runs on way more processors then AIX has ever existed on.
with the flexibility and portability that Linux has to new processors there is going to be a processor specific performance drop.