A reader review points out that some white students have the same problems

Anecdotal evidence here: From teaching and tutoring kids in math of a variety of racial groups, there are white kids who definitely have these problems especially the "twice" v "half" issue. So it could be that students who are weaker at math will have that sort of problem more frequently and the students who speak BEV are correlated for some reason with more weak students. Note that this hypothesis is essentially independent of why those students would be weaker.