The origins of the word punk are quite mysterious, as Cassidy claims in his crazy book How The Irish Invented Slang. However, it isn’t an American slang word of Irish origin. Why not? Well, firstly, the development seems to have been from a word meaning rotten wood used as tinder (dating to the 17th century and found all over New England), to anything rotten (including Johnny here!), to a prostitute, and thus to a male prostitute or a criminal’s apprentice.
Ponach does mean a boy, but it means a very young boy, as in a toddler. And it means that in Scottish Gaelic, not in Irish. (How much influence did Scottish Gaelic have on American slang, I ask myself?) It is pronounced ponna or ponnakh, which is not a great match for punk anyway.
In other words, this is more crazy, childish and badly-researched nonsense from the Great Fraud Cassidy.