Perhaps there is some context this article doesn’t touch on

There is.

This is the most concise and complete summation I could find of the (early) history of the protests against Brooklyn Museum and Anne Pasternak.

https://news.artnet.com/art-world/anne-pasternak-brooklyn-museum-interview-part-2-1409434

Note too that there’s another controversy - regarding the hiring of a white curator for African art - that likely provides the context for the “white supremacist” part of the graffito.