Ask yourself this: how would you feel if someone from another country said that you didn’t speak real English because you don’t speak British English? Kind of preposterous, no? But people do have notions like this; that is, what is good language and what is the best version of a language.
As far as Spanish is concerned, there are varieties just like there are varieties of English. And even within a country, you will find different versions of the same dialect the same way you find, for example, native San Franciscans speaking differently from native Bronxers and from native Charlestonians. But there is no one “correct” or “real” Spanish. A good indication of this is that there are Nobel Prize winners for Literature from Spanish speaking countries, including Spain, Mexico, Peru, Argentina, Chile, Guatemala, and Colombia.
And just in the same way that in Britain you might hear ‘lift’ (elevator), ‘bonnet’ (hood of a car), and ‘biscuit’ (cookie), you will hear different dialects of Spanish use different terms for some basic words (e.g., aguacate [Mexico] = palta [Chile]; guisantes [Spain] = chicharos [Mexico]’ tú [Puerto Rico = vos [Argentina]). And, of course, there are variations in pronunciation and, in some cases, slight variations in grammatical properties. However, all Spanish speakers are proud to be citizens of their own cultures, so we really don’t want to imply that any one Spanish is better than another. As you move from one Spanish class to another, you may meet instructors from various countries who use different varieties of Spanish—and all of them are excellent speakers of their language!