Yeah; the "trick" of the question is "a straight line along a curved surface is actually a curved line", but even this isn't taking into account the Y-axis curv

Yeah; the "trick" of the question is "a straight line along a curved surface is actually a curved line", but even this isn't taking into account the Y-axis curvature of the earth; and thus the assumed-to-be "straight" line you're walking isn't even straight on the globe, its more like an arc along the planet's surface. You can't walk in a universally straight line on the planet. You can only walk in a straight line relative to something. In their example, when they say "walk in a straight line" they really mean something more-like "walk in a radially straight line, relative to the center of the earth, assuming the earth is a perfect sphere, etc" My assumption when reading the text of the question, which I think is most peoples' very reasonable assumption, is that you are traveling straight relative to the eastward direction; meaning, you're re-adjusting to continue to travel east, because that is a reasonable extension of the pretense "you leave Seattle traveling east". Its a bad question that is purposefully bad to trick people.