Since seeing the original comment I have spent the last 2 or 3 hours reading about this. I started on the website and with that document and was confused myself. I also didn't notice the explainers later in the document (the links didn't work for me either).
I watched a webinar linked from the website which covered the material in the document, but the presenters didn't cover a 'what is and what isn't racist in the maths classroom' checklist, rather they showed how to use the document in your teaching/preparation. They did note at the beginning that a level of awareness about antiracism is required, and at the end linked to several sources regarding racism in the curriculum and racism in the math classroom (and beyond).
I had seen a meme recently about 'math is racist' and I didn't get the reference at the time, I'm guessing it's about this foundation. Everybody knows that math is not racist and nobody is claiming it is. The problem is that governments are racist, institutions are racist and classrooms can be racist.
There is a mind view that many people hold which automatically assigns people of colour a lower expectation of academic achievement. The government announces new educational reforms citing statistics that people of colour achieve less academically. These reforms pay for additional teaching time or 'interventions' which amount to a few to a dozen hours of extra teaching which is supposed to achieve something that the five year old was unable to learn in the 36000 hours they've lived so far and 'level the playing field'. Teacher evaluation bars people of colour entry to eighth grade math though they have the grades. Math questions as recent as this decade ask you how many plants of cotton can 400 slaves pick in 120 days or how many slaves can you fit in a slave ship with x and y dimensions.
There is nothing in the brain of people of any race (or gender - maths is sexist too!) that stops them from comprehending mathematics. So why do white boys do math more good? Then go on to earn the good STEM degrees and high-paying STEM jobs disproportionately?
Math focusing on the right answers in the classroom is discouraging for anybody who is already discouraged. Similarly, having a hard time understanding and being afraid not only to get something wrong, but to question the authority can be scary, especially when you are growing up in an environment where questioning some authorities can incite conflict.
As another comment suggested, it is generally good advice for any math teaching. The same goes for teamwork over individual work - being able to explore and approach the problem as a group, and work through it vocally with others as a collective can be encouraging and is also a good opportunity to learn from other perspectives. From the perspective of race, I would agree with the guide which mentions the problems of 'individualisation' in the classroom, how this can lead to competitiveness and further discouragement of those who are struggling.
Most of the principles in the guide seem like best practice to me for any group of young mathematicians. Especially those who do not feel like they can be mathematicians or have any place doing mathematics. Despite its diverse history, success in mathematics in popular culture is associated with white men. That is my view at least, and whether that view has been developed because of my own internal racism or because that is how mathematicians were depicted to me in TV and cinema I don't know.
I think there is a lot to unpack here, I am happy that some discourse on the subject has started here. I am looking forward to learning more about this topic and about myself and those around me and thank the original commenter for bringing it to my attention, though I think they realise themselves that racism in the classroom is a problem which NEEDS to be tackled.
I made a HN account for this so I am sorry if I have missed any commenting conventions. I am on mobile so do not have any citations but would be happy to provide them when I can.