It is also likely that whatever meta information reddit is sending back (in headers or tags) is probably not dated correctly for the time of the origin post.
That doesn't explain why Google lists the old search results as being from this month, while Duck correctly lists them as being from years past.
Google does cache results, and could via comparison with cache notice changes, and claim, the page was updated sometime between.
I've always wondered, how search engines get a hold of timestamps. Locally with a cached sample, like I explained above, parsing a page's content or some metadata? It's not like the HTTP protocol sends me a "file created/last modified date" along with the payload, does it?
That doesn't explain why Google lists the old search results as being from this month, while Duck correctly lists them as being from years past.