Erik, are you so unfamilar with logic gates, that you cannot see how the AND-gate will do its job here?? When no key is pressed, all the rows are pulled-high and the AND-gate outputs high state. If any key is pressed, one of the rows goes low and the AND-gate emits low state, which invokes the interrupt. What is so difficult to successfully analyzing this situation by assuming that the AND-gate is an AND-gate??

Kai