I'm going to bite, even though I shouldn't.
Which scenario do you think happens more. White, qualified workers getting a job over qualified minorities. Or qualified minorities getting a job over white, qualified workers?
I can't really count on your specific situation because there are too many variables. Maybe you and your coworkers weren't as good as you thought you were and were replaced by more qualified people. Maybe they hired employees willing to do the work for less pay. You were too expensive and minorities were willing to work for cheap which is pretty standard here. Maybe you were discriminated against for your race, which would have been in your legal rights to take action against. I have a strong feeling, you didn't.
The fact of the matter is, it's all anecdotal and highly irregular and not representative of the status quo for how racial issues tend to work in employment. To answer your question, yes it would be discrimination if the motive in firing you was purely based on race. It is very unlikely GM would want to stomach the negative press and heat they'd get for discrimination, so I doubt that's all there is behind this story.