It appears that they do not contradict that definition. Please read this article, where you can find the definitions in the context of the crime of apartheid:
https://en.wikipedia.org/wiki/Crime_of_apartheid
There is a section there about definition of racial discrimination, it's not only about race.
"According to the United Nations Convention on the Elimination of All Forms of Racial Discrimination (ICERD),
the term "racial discrimination" shall mean any distinction, exclusion, restriction or preference based on race, colour, descent, or national or ethnic origin which has the purpose or effect of nullifying or impairing the recognition, enjoyment or exercise, on an equal footing, of human rights and fundamental freedoms in the political, economic, social, cultural or any other field of public life.[17]
This definition does not make any difference between discrimination based on ethnicity and race, in part because the distinction between the two remains debatable among anthropologists.[18] Similarly, in British law the phrase racial group means "any group of people who are defined by reference to their race, colour, nationality (including citizenship) or ethnic or national origin"
https://en.wikipedia.org/wiki/Crime_of_apartheid
There is a section there about definition of racial discrimination, it's not only about race.
"According to the United Nations Convention on the Elimination of All Forms of Racial Discrimination (ICERD),
the term "racial discrimination" shall mean any distinction, exclusion, restriction or preference based on race, colour, descent, or national or ethnic origin which has the purpose or effect of nullifying or impairing the recognition, enjoyment or exercise, on an equal footing, of human rights and fundamental freedoms in the political, economic, social, cultural or any other field of public life.[17]
This definition does not make any difference between discrimination based on ethnicity and race, in part because the distinction between the two remains debatable among anthropologists.[18] Similarly, in British law the phrase racial group means "any group of people who are defined by reference to their race, colour, nationality (including citizenship) or ethnic or national origin"