My comment was questioning the phrase "any person on the street" would consider Olivier's portrayal as blackface. I do not believe that is an accurate statement. I have heard discussions by journalists and experienced talk show people of color in recent months commenting on the differences between dark make-up and blackface.
I do agree that Sheng made a mistake (or sin) by not providing his class with appropriate context. However, the word oblivious implies lack of concern which may not be the case here.
How many average, every day Americans of any race would consider the character of Othello to be a black man?