<Maybe widespread enough that China/Japan not only went from east to west but west to east.>
No need to go that far afield. The excavators' suggestion of links with Central or South America is much more likely. Do a quick image search on "Olmec figurines", for example. Some of them look pretty Sumo-esque superficially, but there's no doubt about their provenance. A trade network linking the two edges of the Old World implies absolutely nothing about a trade network linking the Old and New Worlds.
<Just not supposed to be in Indiana.>
Their presence is interesting and very cool, but they're
not out-of-place artifacts in the sense you imply.
