It's been pointed out that McIntyre is rhyming slang for fire and perhaps this is how it got in. But they wouldn't have shouted "fire" when the firemen were already there, so "Arry's version makes more sense. It doesn't matter how you spell MacIntyre - it was originally Mac an-t-Saoir anyway.

What strikes me as amusing is to find dear decent Bob Copper singing such a song. Suppose his pub had caught fire and his regulars began looting it - you can imagine his disgust at such behaviour.