The song, as it stands, appears to have been written for the early music hall; and in Scotland (or even England), rather than Ireland (see various other threads on the subject); although it was evidently based on an earlier, Irish broadside song about a real event that took place in Ireland. That, however, did not contain the familiar chorus.

It may well be that the "cod-Irish" of the music hall song is based on a genuine Irish Gaelic phrase. That doesn't necessarily mean that it was understood as such by whoever wrote the song, or by their audience; or that whatever meaning the phrase may have had in other contexts is relevant to any examination of this particular case.

It's certainly interesting, though. The 19th century popular stage produced vast quantities of "Irish-style" songs, particularly in England and America, many of which included "cod-Irish" expressions and phrases. Some can reasonably be interpreted as deriving from real Gaelic; many more cannot, without very agile jumps of imagination.