This is mostly a placeholder for a better bug report. While debugging #404, I was seeing that even when zoomed in to a very small extent centered over the southern part of the Puget Sound, geometries for Russia and Canada are fetched. We're doing a lot of extra work iterating though every coordinate in these geometries that are far outside the rendered extent (Russia should be far at least, have to check the polys in Canada to see how far south the Victoria poly goes).
This might be because Russia - at least in OSM - has a bounding box that crosses the dateline, and we might not handle this correctly.
As @ahocevar says, Russia's bounding box with the date line wrap overlaps Tacoma.
Canada is fetched because its bounding box also overlaps: the Yukon extends further west and Ontario extends further south.