It was indeed. It was used to disparage Asians modifying their cars and then anyone modifying an Asian car. Because haha Asians eat rice so funny.
Apparently a bunch of the Linux community thought this was a good term to adopt for reasons I don't understand. The mental gymnastics I see trying to make this not racist is tiring.
It's not because they eat rice. Those cars were referred to as "rice burners" because people were insinuating they were running on rice alcohol. Which is still racist, of course.