At an Altan concert, Mairéad Ní Mhaonaigh explained she had researched the phrase 'bacach Shíl Andaí', as she had simply learnt it as a lullaby when she was young, much in the same was as kids learn 'Ring a ring a Rosie', without knowing where it stemmed from or what it actually refers to. It was indeed a reference to the landing in Killala during the 1798 Rebellion or more correctly in the aftermath when many were wounded and became vagrants. 'Bacach' is the Irish / Gaelic for 'lame'. 'Shíl Andaí' is a corruption of the word 'Irlandais', meaning an Irishman in French. That's the mystery solved as far as I'm concerned!