I believe this indicates his righteousness in God’s eyes because God was waiting until Methuselah died a natural death and did not want to let him be wiped away in the Flood which was a judgment of God on the unrighteous.
Sou ass dëst der Zäit, wou Gott an d'Roserei an Strof gëtt op dëser Äerd Ooffahrten matt eraus ginn.