Could be a strange way of expressing his faith. His wife has a new life with Christ now. And this guy does believe that.
It appears by all accounts that they are Christians; but I wonder if they are originally from another faith or culture that might use the Lunar Calendar. Jews for example will basically celebrate birthdays on the solar calendar, but when it comes to deaths they will do the annual mourning prayers for the deceased based on the Jewish lunar calendar death date - so it will change from year to year on the solar calendar.
Just a curiosity.
As I said, grief can cause strange behavior.