The peasants who survived often got evicted. These homeless people did not have the strength to work, so they lay around the roadways and the landlords did not like them cluttering up the landscape. To get rid of them, they made deals to have them shipped overseas to America. A load of timber could be hauled from America to Ireland, and for the return trip the ship’s owner would take a load of useless humans.
I believe that some of those who survived had something special: a genetic mutation that caused their bodies to store abnormally high levels of iron. So while the anemic died, those with the extra iron stores survived.
It probably worked out well, until they got to America, started eating meat, and then reached the Age of Vitameatavegemin.