So what if they're not American GM engineers? They're still GM engineers. Pretty much every car company has regional design offices and engineering staffs that have their products distributed worldwide.

If you want to think of it as a "home market" kind of thing, look at the Acura MDX and USDM Honda Odyssey. Both of those cars were designed by Honda North America and are only built in Canada. Yet Honda imports them from Canada for sale in Japan.