The good news is that we do seem to get immunity for a period of time.
People have said that people who get the milder versions the first time around are more likely to get a second one. So as far as it goes, this doesn't falsify the theory.
The unknown is whether getting the virus a second time results in the same sort of nasty symptoms as the first in larger populations. For this one case, the second event was milder. If that's true in general, then people who have it twice won't be so bothered. Of course, they are carriers, so dangerous to others.