It is rather an insular view to say that only deaf South Africans were affected. You might as well say that only hearing South Africans were affected by Obama's speech, or that anyone in the world who didn't speak English would be affected by having a meaningless translation in their language.
Does anyone think he was experiencing hallucinations in some schizophrenic episode? How, if he was, did he manage to sign at all ? He has been retained by the governing party in the past. His incompetence might never come to notice, but, if it did, do you think the government would care ?