The actual critique - which is articulated in many places - is that "white" isn't an ethnic group with an actual cultural or racial lineage. Instead, "white" was created and exists as the dual to "colored" - a shifting category encompassing many ethnicities that describes their position in a set of power structures, historically colonialism. Consider that "whiteness" has changed considerably over the usage of the term, with many ethnicities (irish, italian) shifting into it as their position in American society (the cultural superpower of the time) changed.
To consider this further, shift the power structures and see how whiteness changes. Who is considered "white" in the historic USSR and contemporary ex-bloc states is radically different than the usage in America at the same time. This is even more complicated in places like Central or South America, India, and parts of Asia. I guarantee that - if you weren't versed with local power dynamics and colorism history - you wouldn't be able to classify who on the street is generally considered "white" in Buenos Aires.