I have to be honest, I genuinely don't know how the Panthers have been doing what they're doing. I can't name a single member of their secondary. I assumed Greg Hardy was the Jenga piece holding them together but they didn't miss a beat without him. Is it Kuechly? Lotulelei and Short? Did Ron Rivera literally sell his soul to the devil?
BTW - those two losses were to @ ARI (where Donald LaFell dropped a 4th and 1 in the bread basket and Steve Smith dropped an open TD pass) and @ NO in primetime (where they're basically unbeatable).
As for how, it's a combination of many things. The Panthers were always competitive, but couldn't get the job done in the clutch, whether that was on the defense (2011) or the offense (2012) - 2-14 in games decided by 7 points or less to start Rivera's career. Then the flip switched on, Rivera got more aggressive on both offense and defense (going for 4th downs and less vanilla/prevent coverages with the lead), and we've since gone 6-0 in games decided by a TD or less.
In terms of the defense, an underrated aspect is just how good Kuechly and Davis are in coverage. It helps alleviate some of the pressure on the secondary.