Ignorance, perhaps, but not necessarily Eurocentrism. Viewing Chinese as a single language – often with Mandarin as a prestige "dialect" of it – is a common position of Han nationalists.

Attempts by some Western linguists to treat the Chinese varieties in a way that emphasizes their mutual unintelligibility and downplays the importance of the common writing system, have even been attacked by said Chinese nationalists as being "anti-China". It is very similar to how, decades ago, many Russians bristled at attempts by foreign scholars to view Ukrainian as a language in its own right, since their position was that Ukrainian and Belarusian are simply some aberrant or low-prestige forms of the Russian language.

But just in case, I want to make clear that by "the official dialect of Mandarin", I meant the one dialect of the Mandarin language that is officially recognized by the CCP. Whereas by "Chinese" I meant the language spoken by almost everyone in China nowadays, i.e. Mandarin (I did that because I was replying to a comment that was talking about Chinese, so I used their wording).

Thus, with a correct understanding of my intentions, the equivalent for English would be "Unless you limit yourself to the official dialect of British English, English also has lots of inconsistencies ..." (where the official dialect would be the Received Pronunciation).