The "genocide" portion comes from the fact that:
* Ireland's dependence on potatoes for subsistence was due to forcible appropriation of essentially all arable land by the English government, which redistributed it to absentee landlords.
* Despite clear widespread famine conditions, England continued to export food out of Ireland and maintained an official policy of not intervening in the "free market" of Irish exports, at the documented cost of hundreds of thousands of lives.
* Meanwhile the English government did see fit to interfere with foreign aid to Ireland and even actively refused large donations and shipments, allegedly on grounds that it would be insulting to English pride for other nations to do more than England itself.