Chinese dialects are totally separate languages, in some cases only distantly related. A Mandarin speaker with no previous exposure to dialect X would find it incomprehensible. It'd be like calling Swedish and Portuguese dialects of the common language “Euro-nese” (as was once the case with 'vulgar' Latin before we started calling it French, Spanish, Italian, etc.)
The Chinese government calling these languages 'dialects' is Orwellian new-speak that makes “language unity” sound like speech therapy instead of the linguistic genocide that it is (a practice which, to be fair, predates both Orwell and Mao).