Here's how I'd state my interpretation: "Statistical analysis suggests that supercentenarians are becoming more common. However, even as their numbers increase overall, the number of people aged beyond 115 is negligible."

The abstract for the paper itself ( http://www.nature.com/nature/journal/vaop/ncurrent/full/natu... ), seems to only discuss the statistical existence of an aging limit, not the biological mechanism(s) causing it.