Mixture of "allegedly" and "urban legend has it that". Often followed by an unbelievable "fact" or story, which is very likely to just be a made-up story or one that was passed by word of mouth and changed in the process to make it more interesting or spectacular.

Probably first used by Jalen Rose on his podcast on Grantland Channel in the video "Champagne and Campaign Hall of Fame".

When you eat dirt for the first time and leave your family to build a shack in the woods

When something is according to urban legend. A mixture of urban legend and allegedly. Created by the patron saint of Champagne and Campaign Sir Jalen of house Rose.