Not just Japanese, but East (and North) Asian in general. In fact, because of the genetic similarities, and of course lack of samples, a lot of DNA profiling lumps Indigenous Americans and East Asians in one group.

I have Native American ancestry, and was doing research on our history and was shocked to see the grouping, but also not so shocked, as it makes sense.

The Athabaskan languages (Slave, Gwich'in, Navajo = Dene, Apache, Chilcotin, and a host of others) have been shown by linguists to be probably related to the Yeniseian languages of central Siberia. If this is true, it does not however mean that the other Native American languages are also related to Yeiseian, since the Athabaskan languages are not known to be related to any other languages of the Americas.

But of course it's likely that the ancestors of the other Native American groupings did come from Asia, via the Bering Strait, which at various times was above water--there are just no plausible connections between these languages and languages of Asia, which is not surprising given the time depth.

Bering Strait

I figured. I just find it super cool to see contemporary signs of something so far back in history.

Yeah ... but which way? (And I'm betting on the Aleutians)