I understand that she might find it infuriating, because 2/3 of it consists of repeated worksheet pages about planning, executing and critiquing improvements in math education.
The other 1/3 of it, however, is largely discussion of bad math teaching, framed as racist math teaching. Most of it simply points out that bad math teaching is frequently authoritarian math teaching.
I find the framing grating and the discussion of pedagogy insufficient -- I would prefer about ten times as much -- but this is a calendrical worksheet book, not a text.
I suspect Weiss [edit: Klainerman] did not read the document he is criticizing, or didn't understand it.
I think the framing you mention is part of a broader effort to understand that in the U.S., authoritarianism is, overwhelmingly, racism. If you can think of a large, structured system in the U.S., you can usually think of ways that it (for some reason...) has worse outcomes for non-white people.
The outrage is really about mandated bad teaching environments. There are also very bad side effects for minorities, but calling it racist, when the culture is overall about domination, is missing the target.
"As awful as this is, the fact that it's funded by The Gates Foundation makes it even worse. So when Bill isn't trying to save the world from Climate Change or drive the world batshit crazy about Covid he's spending his money on racist initiatives..."
All they need to validate their misguided outrage without having to read a damn article. Wish Weiss would start a series about lazy pseudo-intellectualism feeding all this tribalism.