It's probably a glitch. JavaScript and several programs calculate date starting from 1st of January 1970 (31st of december 1969 in American timezone).
Perhaps some system upgrades to ATS have inadvertently reset the visit date back to 0 - that is, back to 31st of december 1969.
edit on 29-1-2016 by swanne because: (no reason given)
I think it's just a wonky bit of code that got left in from one of the site iterations, something benign that would be more difficult to fix than to
just let stay in. Kind of akin to why some of us older members have millions of stars.