Don’t you realize how silly, or even desperate, it sounds? He went combing through every and any cultural custom and found something that rhymes. This now becomes ‘proof’? Yes, making an specific shape using among other items, a key, is a far cry from making a key out of the whole bread.
If indeed the only reference found is from Ireland then the joke and bias is obvious.
Regardless, as I said earlier, it really doesn’t make any difference how it originated historically. It was never meant to follow their customs and surely today it is being done with Yiddish intentions.
Many of those complaining or ridiculing this Minhag probably subscribe to the reason given in Moreh Nevuchim for Korbanos. That would be way worse. In that case the custom was in itself an act of worship, and still it becomes sanctified through reinterpretation.