More wordplay than anything else. “Go east and then continue straight” is different than “Go east and continue going east”. Results from each are more predictable than misunderstanding the prompt.
Even if the prompt had been "Imagine a traveling from Seattle along a Great Circle path that initially heads east" to take out the "trick" part of the puzzle, I think I probably would have had a hard time visualizing the path without a physical globe in front of me.
Yes, if it had just mentioned that it meant a great circle, I would have felt like it wasn't such a gotcha question.
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If that was the question you’d hit Canada before the Atlantic.