It’s the UCL group’s estimate that 60 million people were living across the Americas at the end of the 15th Century (1400-1499)
Wikipedia:
In 1492 the native population of North America north of the Rio Grande was seven million to ten million.
Hmmmmmmmmmmmm...Quite a difference there...
So this UCL group must be including Caribbean Islands, Central America, South America, and Mexico...