True, and Mandarin would be the better word to use here. Mandarin and Cantonese are for all intents and purposes separate languages. They are more different than English and Spanish.
Standard Chinese can be spoken in Cantonese, but while understandable, it is never done, in contrast to Mandarin.
In recent years written online conversations (like blogs, Facebook posts, instant messages) by Cantonese speakers are increasingly written in Cantonese instead, and this is slowly spreading to more "formal" media such as books.
Source: I'm a native Cantonese speaker.
They're still a lot closer than English and Spanish or even French and Spanish (https://www.ezglot.com/most-similar-languages.php).