This happens fairly regularly it seems. Why would it be appearing higher in the search results?
For every x good questions, there are n x mediocre dupes. Your search terms turned up one of the dupes, because the wording matched closer to it. By the exact same logic, the original poster didn't find the original because they worded it sufficiently differently.
Stack Overflow, and in fact all SE sites at a critical size, must rely on both depth and breadth to successfully bring in visitors. Broad search terms land users on many questions, but they in turn funnel toward one deep canonical post. Everybody wins.
Lastly, remember that anonymous visitors don't land on the duplicate. They are redirected directly to the final destination. The funnel does work efficiently.