Feels to me this should be an option set by whoever closes the thread. An automatic solution has potential for false positives.
Although in your example case, it’s pretty clear what the “real answer” is. Maybe search should be aware of multiple closed top results, and only then analyse them for a common “real answer” link, which could be promoted or highlighted.
eg.
(excuse the ugly MS Paint text)
I suppose it depends on your philosophy for the search tool. Are you trying to find “the answer” or a specific topic?