I can't really see what difficulty there is about the meaning of this song. Once you've got the bit about the height of horses being measured in hands, and considered the possible ambiguity of the word "lie" , the meaning seems fairly obvious. Jimmy MacCarthy might be able to tell us that it was connected with some event or relationship in his life. This would not change the meaning of the words of the song. At best we would have another set of words telling us what he intended to mean. We bring our own images to it, imagining stories that gave rise to these words. None of this changes the meaning. The words are there, simple words, and they are easy to understand.