The extinction doesn't seem to have happened 50k years ago in North America. That seems to have been made up by whoever wrote the headline. The date of 50k years ago does not seem to appear anywhere in the linked academic paper, does not correspond to climate change at the start of the current interglacial, and does not correspond to evidence of the arrival of humans in North America. Even the body of the phys.org article doesn't say the extinction happened then.
There were wooly mammoths alive in 2000 BC, 600 years after the Great Pyramid was built. There is evidence of humans and mammoths being in north America together.