The Western Hemisphere. General term for the Americas following their discovery by Europeans, thus setting them in contradistinction to the Old World of Africa, Europe, and Asia.
Wapato is super common on the lower Columbia River and in the lakes and sloughs around there. It also occurs up in BC in several localized areas IIRC. For people who eat largely meat and some fruit and vegetal matter, a good dose of starchy carbs is just what the doctor ordered. People really crave it.
Wapato tastes just like a potato, it is a step above camas on the coolness factor because it does not need to be cooked prior to eating it. It is easy to harvest, and the more people harvest it, the more it spreads. After the advent of food storage in this area, wapato proved a great asset to people who lived where it occurs, it stores well in underground caches for months on end, and it became a sought after trade good (mostly post-dating the BC site the article talks about). It does occur in sites prior to that though, some of the older examples go back some 6,000 years IIRC (it's been awhile).
The statements of farming at 3,500 BP, amazement at finding wapato at the site, etc. are just sensationalist crap. But then almost every news article on archaeology is these days, between the archaeologists (they don't even sound like archaeologists in this case) quoted and the journalists they just get way out of whack.