It was cooked at 400'F until the meat probe was at 165'F - From the BGE Recipe book.
Just converted that to English money and that means cooking temp of 205C until the meat probe was at 73C - I wouldn't do a chicken in my kitchen oven that hot and whilst 75C is what env health will tell you is safe (to protect the public) I would regard that as "buggered" (Northern English expression), especially for the breast meat.
Try going lower and slower at 125C, you won't get crispy skin (for that you need to be over 150C) and hit 70C close to the bone. You'll have to discard the skin but the meat will be supremely moist.