I knew that one because the parade was broadcast on TV when I was growing up, along with the Rose Parade. I'd never heard of the chocolate one but as you say, there are only so many possibilities.
From Wikipedia: “The parade traces back to mid-17th-century roots, blending elements from Swedish, Finnish, Irish, English, German, and other European heritages, as well as African heritage.[4][5] The parade is related to the Mummers Play tradition from Britain and Ireland.[6] Revivals of this tradition are still celebrated annually in South Gloucestershire, England on Boxing Day along with other locations in England and in parts of Ireland on St. Stephen's Day and also in the Canadian province of Newfoundland and Labrador around Christmas.” Some sources say New Orleans’ Mardi Gras comes from the same roots.
Tons of fun -- In the purest of Philadelphia spirit, parade goers come out to throw snowballs packed around AA batteries, boo viciously at small children, and inhale Cheese Whiz until they black out.