You are probably annoyed that it is so expensive

Yes apparently people still buy that type of clock. And looking at French auctions people pay handsome sums of money for that type of clock.
I usually don't participate in controversial or political discussion. Some people today are overly sensitive today in my opinion. Is a 220 year old clock reflective social issues in the 21st century? To some people the answer is "yes".
To answer your question literally,
The Oxford Languages definition of "racist":
adjective
- characterized by or showing prejudice, discrimination, or antagonism against a person or people on the basis of their membership in a particular racial or ethnic group, typically one that is a minority or marginalized.
At the time the clock was made (Empire), it was more exotic than meant to be antagonistic towards Africans. Perhaps the motif is discriminatory, but it is a product of the times. The clock was made to be purchased by the wealthy class. As well, it was a display of the skills of the bronzier, to show a contrast of color. I have seen many blackened bronze accented clocks that do not depict Africans. But apparently still purchased by the wealthy class.