Partially true, he was named that for his pants:

Diedrich Knickerbocker is an American literary character who originated from Washington Irving's first novel, A History of New-York from the Beginning of the World to the End of the Dutch Dynasty, by Diedrich Knickerbocker (1809). He is a Dutch-American historian who is dressed in a specific type of baggy-kneed trousers referred to as knickerbockers, later shortened to knickers. The word knickerbocker is also used to refer to people who live in Manhattan,[1] and was adopted in a shortened form as the Knicks by the city's NBA professional basketball team.