Thats the dude who plays Ser Barristan Selmy, the one who argued with D&D hard about killing off the character.
That's not some wild fan theory, that is a guy who loves the books and knows GRRM.
It's still an absolute lie that he's finished books 6 and 7 though. No idea why the guy would say that.
http://georgerrmartin.com/notablog/2019/05/13/idiocy-on-the-internet/
"I will, however, say for the record — no, THE WINDS OF WINTER and A DREAM OF SPRING are not finished. DREAM is not even begun; I am not going to start writing volume seven until I finish volume six"

