Easy peasy, famines were commonplace in Spain during the Middle Ages (not sure how about part of it that was controlled by the Muslims though, but i don't think it was much different). During the Middle Ages, famines (and epidemics) were the natural regulator of population and were seen as a normal thing. By the XIX century of course, things were very different....

In Spain at the period, there were no famines because people kept emigrating to the colonies. Ireland was itself a colony. That's the difference. In Eastern Europe where countries didn't have colonies, famines were a norm.

Irish one is seen as something special because it happened in the West, and because overpopulation there built up for a considerable time being allowed by potatoes farming that for the time being, provided plenty of food allowing population to build up. Then it backfired.

As for local populations pre-existing in the colonies, sure they almost all died out. To a much larger proportion than the Irish, and sometimes, went entirely extinct. That is the normal part of absorbing new lands. It's just that Ireland was Christian almost since Christianity became a thing, and was never "discovered", that made it special. But we shouldn't pretend like it wasn't normal or in any way exceptional overall. Genocide is a natural way in which nations interact.