If no cuts or stone tool traces are fount with the remains, then I vote for this animal being a victim of the meteor strike(s) recorded in the book at comment 2. A lot of animals and humans probably died back then, but it took another 3,000 years for this type of elephants to finish dying off in North America.
You may be thinking of ‘dwarf’ mammoths which apparently persisted on arctic islands off Siberia until 2-3 thousand years ago.