Because of a glitch in the UNIX timestamp that ended up assigning that quiz a timestamp of zero.
The UNIX timestamp starts at midnight UTC/GMT on January 1, 1970, but because JetPunk uses the Eastern Time Zone, the site shows December 31, 1969 as the date.
The UNIX timestamp starts at midnight UTC/GMT on January 1, 1970, but because JetPunk uses the Eastern Time Zone, the site shows December 31, 1969 as the date.