Why skin is black because they have high melanin content on their skin which protects them from UV radiation effects but it doesn't mean that skin colour decides the immune of a human body and corona virus is not spreading through skins it more likely due to respiratory so that chinese doctor lied. 
Exactly. It's absurd and racist to suggest that superficial differences such as skin colour are relevant. "African immunity" has been discussed before, and (I believe) is due largely to a lack of direct air travel from China:
The Chineese govt. says uptil date there has been no report of an nCov victims in Africa except for those in foreign countries. The report further stated that this could be to the hot weather. rendering these enviroment completely nCov attack-free zone.
nCov started in China. Cases in other countries have spread from China.
If there are zero cases in Africa, the most obvious explanation surely is that there are relatively few people (and therefore relatively few infected people) moving from China to Africa.
Look at the distribution by country (first chart below, as of today).
What you see is a lot of cases in countries close to China, and some cases in countries that have a lot of international travellers. The USA has over 50 cases, Mexico has none. Both countries have over 100m inhabitants. Are Mexicans somehow immune? Or is there more travel between China-US than between China-Mexico?
Compare the nCov cases chart (first below) with the list of China Air international destinations (second below). The parallels are striking.
https://www.ecdc.europa.eu/en/geographical-distribution-2019-ncov-cases
https://en.wikipedia.org/wiki/List_of_China_Airlines_destinations
