Based on years of intense study, I can state with confidence that the person you saw on the short video last night, is the authentic KC. Everything else is an elaborate pretence. I believe he speaks exactly like that when he's with members of the family, or at the bank or the doctors, or on holiday abroad, or relaxing at home. The reasonably well spoken and well adjusted person we see when he is performing live is a fiction and a product of his feverish imagination.
I have in the past stumbled upon him speaking like that in the butchers in Crail. When he realised I was behind him, he hurriedly changed to his pretend refined voice. The butcher got a bit of a surprise with that, knowing KC as he does.
I leave you to draw your own conclusions.