Other than the Willow Garden and the "young 'lovers'", I don't see much connection...the tune (according to the forum) is Rosin the Beau which is quite different from Down By the Sally Gardens. The Traditional Ballad Index [ http://www.csufresno.edu/folklore/BalladSearch.html ] has a reference (search for "Willow Garden"), but no date...a date would be interesting for comparing the timeframes of both songs.

(..however, it is no surprise that lots of the notes are the same since there are only 7 notes to work with (plus their sharps and flats..) BIG SMIRK!