Well, it's going to be more pure than Spanish in Mexico, Argentina, Costa Rica, Andalusia area of Spain, Catalan area of Spain, Basque Country, Galicia region, etc etc. Castilla is just the region and Salamanca is known for it. It's just a simple statement. I'm not trying to prove anything, but to think they speak better Castilian Spanish in other areas of the world is not accurate either. Like I said with my experience, all my friends in Spain told me there is not better place than Salamanca to learn Spanish. That's the reputation it has.