I cast the final closevote on What is different between “ellipse” and “oval”? just now, citing "Lack of research" as my reason. But just to reassure myself that the "difference" really is easy to look up online, I copied the title and pasted it into a google search.
Unsurprisingly, I guess, I found an 7-year-old ELU question Are there any differences between “oval” and “ellipse”? high in the list of results.
But I was a little surprised to see that the earlier question hasn't been closed (in fact, nearly 50 votes have been cast on that page, and the question has been "protected"). Which strongly implies that my closevote on the later question was a mistake.
Even if I had found that earlier question before closevoting, and had cited it as a duplicate, my reason would have been "outvoted" by the preceding 4 closevotes, so it wouldn't really have made any difference.
So what I'm asking here is the question posed in my title. Without mod intervention, the only way I know to "fix" things is if 4 other users were to join me in voting to reopen the later question, then we could vote to close it again for the right reason. Which would probably have to involve more than just the original 5 closevoters, since I think the system gets sniffy about repeated open/closevotes from the same user.