It's not actually NewsBlur's fault. That feed probably writes its own RSS feed and screwed up the datetime for a story. It stems from the fact that the UNIX epoch (0 seconds) is January 1st, 1970. They probably published a story, didn't add the correct story date, and published it with a timestamp of 0, which gets translated to January 1st, 1970.
NewsBlur, for its part, checks if there is a date and sticks with it. If there is no date, it just assumes the current time (and a number of feeds publish with no date on their stories -- Hacker News being a prominent example). In this case, the blame lies squarely with the feed publisher.
Also, as you can probably guess, you would easily be able to backdate a story, so don't trust story dates as anything more than meta data provided by the author.