Standard bourgeois nationalist line. Rather than viewing socialist society as the only context in which a truly multinational, multiracial society can exist with real equality (USSR during its revolutionary period and Cuba being prime examples) they are uncritically accepting the bourgeois conception of race as scientific and irreconcilable, and of nation as only being able to persist in a "homogeneous" (a word/conception which inherently requires the idealist erasure of internal contradictions) society.
The idea of the "homogeneous" nation or state is absurd on its face and is a historical falsehood. Even the so-called "homogeneous" status of the Nordic states (which many reactionaries cite as the reason why their social-democracy "works", as opposed to social-imperialism), is a mythology constructed by these states as a means to both legitimize themselves and pave the way for the bourgeois/fascist project of exploiting the land and peoples they control. Ask the Sámi people how homogeneous a society Sweden, Norway, or Finland is, I'm sure they'd be happy to enlighten you as to how many were murdered to achieve that illusion. It's especially absurd to view the "multinational, multiracial" concept as nothing more than a means to "Americanize" Korea. The United States itself actively seeks homogeneity despite the claims of the "progressive" wing of its fascism. There are tens (if not hundreds) of thousands of indigenous women alive today
who have been sterilized by Federal and state governments against their will. Black culture is wrung out and commodified for all its worth and discarded when white people are finished with it. Immigrants are told that we are a "melting pot" while their cherished family and cultural practices are regarded with fear and revulsion until they warp them into barely-recognizable husks more palatable to white tastes. In every instance "homogeneity" is nothing more than a mask the dominant nation puts on to pretend it doesn't need to come to terms with its own chauvinism. "Why work on myself?" it says, "everyone agrees with me anyways!" A so-called "Worker's Party" adopting that conception and not doing an iota of work to analyze the conditions of its greatest global enemy (evidenced by its absurdly out-of-touch view of the US) is deeply alarming.
Their conception of "multiracial" is similarly alarming. Like >>1602410
said, there is a legitimate critique to be made of these concepts in the context of bourgeois society, where they cannot genuinely exist and instead act as smokescreens for national exploitation and imperialism. For those of us fighting for the construction of the dictatorship of the proletariat it's critical that we have a firm conception of what's scientific and what isn't. Race, in any respect, is an unscientific term with no material basis. Bourgeois forces hastily and messily redefine it constantly once each conceptualization is revealed as unworkable. First it was about spirit (or original sin even!), then it was about skull shape and IQ, then it was about genetic traits, and now we're throwing in mitochondrial DNA. Whatever arbitrary correlation pseudoscientists thought they found would be magically the reason why one group in western society is dominant over all others, and the differences between the "civilized" and "uncivilized" the reason why social strife persists. No, class struggle cannot possibly be a thing, there aren't material differences in interest between different sections of production, you see Stalin was really just a dumb Asiatic Georgian and that's why he was a communist! Yet constantly bourgeois ideologues are hounded by the age-old (and correct) statement that "correlation doesn't equal causation" and are only able to maintain race as an immutable, "scientific" trait by restricting the masses view of the greater context that these trends arise in. Race quickly falls apart with even cursory knowledge of the genuine causes of inequality and destitution in capitalist society, and on the intellectual front the emerging study of epigenetics is likewise challenging dominant pseudoscience.
All of this is to say that the principal relevancy of race to the communist movement is in seeking reparations for what racialized people are owed from the bourgeois class (as part of the wider project of the oppression of that class in the DotP) and actively challenging the racialized superstructure in bourgeois society which maintains a class collaborationist attitude among many. The correct response to western "multiracial" narratives is to correctly state that only socialism and later communism can actually bring about such an equal and equitable society. Instead, the Worker's Party accepts bourgeois pseudoscience as fact and, rather than fighting against the west on the home turf of the scientific working class, has decided to fight on the terrain the west has chosen for them. They're being baited into a trap position to alienate them from the wider movement, and fell for it hook, line, and sinker. I would be less harsh about these critiques if the Worker's Party still showed any real interest in taking part in these international line struggles and actually sought to be a part of the International Communist Movement, but they have made it clear that they are uninterested outside of performative greetings and window dressing.