As I understand it, "clanker" was a term created in star wars for people to refer to droids in a deliberately derogatory way. It is quite literally a racial slur created in a fictional universe, which people are now using against AI programs. Even I don't like it, and I'm pretty heavily anti-LLM
There are many races in star wars, not all of which are humans. You could be racist against Gungans or Twi'lek if you wanted. Droids in star wars could be interpreted as fairly close to human in some cases, but are used as a slave race in probably a majority of cases