Are autoimmune diseases more common in black people or there's no difference?

Some are. There are certain diseases that are more common in black persons than not. The ultimate autoimmune disease - systemic lupus erythematosus - is more commom in blacks than non- black persons but many other autoimmune diseases do not show any racial preferences.
Some yes,some not! Certain diseases considered autoimmune occur more frequently in one racial group compared to another, and even within certain nationalities within a specific race. Sarcoidosis, sle, and gout are more frequent in blacks. Spondylitis, psoriatic arthritis and psoriasis are more likely in caucasians. American blacks have a 20-30% mixture of caucasian genes, and different in immune probs than africans.