Weird to call it "Spanish". Catalan is also "Spanish" (though you'll find a very small number of speakers in Southern France). Usually Catalan is opposed to Castilian.
The common term for the language we're talking about here is Spanish (in the English language), which is a distinct language from Catalan. Catalan may originate in Spain (and thus could be called Spanish-the-adjective, though that doesn't seem terribly useful conversationally), but it is most definitely not a dialect of Spanish-the-language.
Castilian Spanish, when used in English, is often used to denote the dialects spoken in Spain, as opposed to the dialects spoken in Latin America. This is not the topic at hand here, so there isn't much point in calling it Castilian (especially since many English speakers would not be familiar with that term) over Spanish.
