Indeed, they do claim that.

It's objectively wrong, though. Indeed, the very same people implicitly acknowledge as much when they complain about, for instance, the global hegemony of Enlightenment values.

Like it or not, although culture is not identical across countries with a predominantly white population, there are some really significant cultural similarities (and were pre-racism* too, due to geographical proximity...just like Asian cultures have similarities due to geographical proximity that co-occur with a somewhat characteristic physical appearance). Besides, culture on Okinawa isn't identical to that in Hokkaido, nor is culture in Tunisia identical to culture in Pakistan.

Of course, if you split people up, nobody has any intrinsic culture. People are just people. We learn our culture. It's all an accident of location and history.

And even if it were true that there was no "white culture", it still doesn't matter! When you pick a word that cannot be divorced from a widely-recognized immutable characteristic of that person and associate that word with all sorts of horrible actions by people with that characteristic (but not the neutral and good actions that represent the full complexity of the human experience), you cannot avoid the association of people displaying that immutable characteristic with those horrible actions.

Anyone who understands why the word "blacklist" should perhaps be deprecated should have no trouble whatsoever understanding the message sent by using the phrase "whiteness studies" to mean what it does.

* - Addendum: people have always been racist in some sense. I mean the specific "white man" vs "primitive peoples" type of racism used to justify colonialism once "conquest is glorious" was no longer cutting it.