In this case it will default to globalization settings of your APEX session. If you have your application set to English and "Application Language Derived From" set to "No NLS", you'll get double-quote enclosed data, separated by commas. If you set the "Application Language Derived From" to "Browser (use browser language preference)" though, then your globalization settings will indeed be derived from your browser. So if you change your browser language to e.g. German, your CSV will be downloaded using semicolons as separators and your date values formatted with the default German date format.