Stan,
I have never read a reason for him doing that, I guess it was an opportunity he had and he took it. Most Irish have a general dislike for the Irish. At least in those days they did and from all the problems that the Brits have had in Northern Ireland they still do.
The Irish are a very proud people and they don't like to be pushed around. My geat grandfather Alex even donated .70 cents to the cause of freedom in Ireland. I often wondered if Great Grandma Ellen knew he had that much money. :)
Frank