This is grossly incorrect. The proper classification, to a linguist, is that Chinese is a family of language varieties, and Cantonese and Mandarin are languages within that family (among many, many others) that share a mutually comprehensible writing system, Traditional Chinese. There is no single spoken language that is correctly called "Chinese", and Mandarin isn't entitled to that default status just because it commands vast numerical superiority on the mainland and has the official backing of the PRC, which has never had a stellar record of respecting linguistic, ethnic, or cultural minorities that are not Han-ethnic Mandarin speakers. The claim that Mandarin is the one true Chinese while other languages like Cantonese are regional vernacular offshoots is an extremely familiar misperception spread by PRC propaganda and out-of-touch apparatchiks in Beijing, and in the global diaspora, where Cantonese is the dominant Chinese language in many countries, it doesn't reflect reality at all.
That these misperceptions are still circulated is, in itself, a compelling reason to vigorously resist the PRC's hegemonic language programme. But I'll refrain from stepping further into that mire, as an announcement thread about Nintendo localization is not the right place. (And to be fair, a lot of innocent confusion stems from poor non-technical translations of words like "dialect" that do not reflect their actual definition in linguistics. Popular understanding of language can be quite sloppy.)
