I searched DuckDuckGo just now and a StackOverflow question came up as a search result. Instead of a meaningful page description or snippet, below the DuckDuckGo search result entry appeared the following:
Back to the future! Just like the '90s, good things have to come to an end. If you want to switch to the current site, you'll find the option here.
This is not helpful for users, and should not happen again. I expect it will be a short-lived problem, as the throwback theme seems to already be deactivated.
BTW, it was likely an accessibility problem as well as an SEO one.