This is somewhat a mixing and matching of history and the historical elements of a profound sort that left a mark on things. These Indians were present during the flood period and were rescued because they were warned in advance the waters would rise, but this is not what annihilated these creatures, that was done by virtue of the divine realm in answering the plea of these suffering humans who were indeed plagued, again and again, with many disappointments and the loss of property in painstakingly constructed dwellings to provide islands of safety in the air, so to speak, to keep them out of reach of the tigers, only to see them attacked and destroyed by the quite aggressive mastodons. As these animals were extraterrestrial in origin and brought to Earth specifically for the purpose of pressuring humanity and causing widespread destruction and suffering, it was feasible for the divine realm to see to their removal in response to the outcry of humans in their grief and mourning of their fellows ravaged by these beasts, and this was seen to be needed to provide a turning point and stem the tide of attrition.
This could easily have been a massive worldwide annihilation of humanity all on its own and as has happened time and again, the divine realm was moved to disrupt the plans of the interlopers to minimize their reach. This they interpreted as the inadequacy of these aggressive creatures to do the deed fully and was not seen to be supernatural in thwarting their plans, but rather the hope that dominance of these species would win the day and so disrupt human plans and take lives directly, that this would tip the balance towards annihilation. And when this failed to happen, they simply wrote this off to an unexpected and somewhat inexplicable weakness in their plan. They attributed the eventual reduction and disappearance of these creatures altogether, to the lack of adaptation to the Earth environment.