Now I'm confused. Here's what Wikipedia says. The last ice age was 11,000 years ago, so presumably they should have spread back out northwards since then... or maybe they needed to evolve the ability to survive in the cold first, which they haven't had time to do? IDK.
I'll edit the title to be more accurate. I don't necessarily see a conflict between the fine details of what the article says / what Wikipedia says / what Smithsonian says, but my title is misleading and the careless way I read the article led me to totally misunderstand it.