Why do I need to know what être chocolat means?
It's one of those irritating expressions when you understand all the composite parts and yet you're none the wiser about what the expressions means when they're all put together.
So, what does it mean?
The literal meaning is, of course, 'to be chocolate' but as that doesn't make much sense, it has a different meaning altogether.

Likely an insult towards blacks. Makes far more sense than the 2 proffered explanations.