So, the name "Methuselah" can mean either "Man of the Dart" or "His Death Shall Bring Judgement"
The biblical Methuselah died the year before the flood. He is the oldest human documented in the bible (at almost a millennium old). He was quite probably a Cainite. The title of "Methuselah" may have existed in the First City, and history has simply lost this elders names.
The death of the Methuselah (whose death shall bring judgement) may be the trigger event for the flood. I imagine that he was practicing magic, blood or otherwise, specifically focused on water. A Proto-Thaumaturgy, if you will. When he died, his childe or sire simply said "Fuck you all" and dropped something akin to an Eighth level or higher Neptunes Might ritual on the world. The expenditure of energy required for this may have extinguished the Kindred, or they may have killed themselves or simply fallen into torpor.
Alternatively, Methuselah was a favorite of Ravnos, and his death made Ravnos choose to "cover the world in his tears." So he made us all think he had.
