The lady had a thick accent, and mccain didn't understand the Q.
Instead of asking her to clarify, and either offended the spanish voter base/hispanics, or appearing to be old, deaf, and confused, he just gave a canned answer.
Perhaps he just assumed with her accent that it'd be safe to guess the hemisphere. He didn't know the Q was about Spain and answered anyway. He should have more carefully chosen who he handed the mic to, but then again, we all know how good he is at vetting people...