Basically Isidro was a farmer dude. He arrived in Andalucia (southern parts) and brought the locals bread 'cos he thought they might like it and it would stop them killing him. In exchange they gave him some ham as a gesture which he accepted and probably stuffed it into his bread and made a sarnie (accompanied possibly with some spicy Nik Naks).
They may have killed him after he had eaten the sandwich as he had gained a false sense of security. The moral of this tale is to never let your stomach make major decisions.