Yes and No.
I think this an interesting observation. I am a mix but I am multiracial. My father is East Indian and my mother is a combination of mostly American Indian and French. On the French side is where the curly hair came from. My maternal grandmother was from Lousiana. She was mostly French but had some African American in her background. But I also think my father has some curly heads in his family as well. I am about 95% of races that would normaly have straight hair, but with genes you never know. I would say it is probably more common that mixed race and middle easterners have curly hair, but there are still a lot of other people that fit the 3b description as well. Good point though!