I think the producers wanted to create a 'little england' attitude towards non-whites by pitching a black couple against a yorkshireman in a popularity contest - in Yorkshire! A thinly veiled disguise of exposing racism packaged up as a competetion to win a house. It made good TV.
God know why they would be anxious of meeting a black person - meethinks the interviewers did a very good job of manipulating the locals with loaded questions, NLP techniques and clever editing to get the required reaction from them.