I suspect you may have created a poor-man's slow-cooking environment in there. You had meat, and liquid, and a median temperature of around 200° F, and you probably also got the bird close to "done" during the first broil, before you even left the house. This is obviously easier to do when the meat is covered (was it in a covered roasting pan?) due to the steam, but the oven does provide some insulation to begin with.
Technically when slow-cooking you should theoretically be able to speed up the process by quickly bringing the meat up to just below doneness/moisture-loss temperature (130° F) and then switching to a moisture-preserving slow-cook method like braising. I think that's what you accidentally did, but it's hard to say for because nobody was there for an hour and it sounds like you didn't check the temperature before the second round in the oven.
My guess is that the second roast at 400° F was probably unnecessary, and that the bird was already done, having been cooked in a very slow roast.
I'm pretty sure it wasn't the basting that helped. It seems to be regarded as a myth these days that basting keeps the meat moist, because the baste really doesn't penetrate the skin (and it's not the skin you're worried about). Basting is done to add flavour, not preserve moisture.
The recipe itself also doesn't strike me as anything special in terms of keeping the bird moist, aside from having a relatively short cooking time (as with any grilling/broiling) and letting the meat rest afterward, neither of which really apply in your case. It was probably the slow heat that did it.
Chicken juices contain a soupy mix of proteins including haemoglobin (which gives blood its red colour when mixed with oxygen), and some myoglobin (which gives red meat its red colour when mixed with oxygen). Up to about 140F, they are unchanged, but heat them to between 140F and 160F and they lose their ability to bind oxygen and so their colours change. So if your juices are running clear, you know the temperature is at least higher then 140F and probably closer to 160F if they are indeed clear.
The question of what is 'doneness' is an interesting one. For most foods, doneness is a question of taste. After years of eating my chicken at 'at least 140F', I really like that taste. We usually cook foods to improve their taste, texture, nutritional value; very few foods traditionally kill or harm us if they are not cooked (cassava, certain beans are notable exceptions). Heating to 165F is recommended not for taste but to kill organisms such as salmonella - a tricky blighter that lives inside the cells of some other creatures and so can't be washed or peeled off.
I'm pretty sure that I'm the first generation cook in my family to own an instant-read probe digital food thermometer, so why is this now necessary? Well I may also be the first generation where salmonella in store-bought chicken is considered a saleable product and something to be cooked out by heat, rather than designed out by good farming and food handling practice. The 165F statement from food safety bodies was brought in to deal with such issues.
In France, there are still plenty of people who like their chicken very pink. With my own grown chickens, I will cook them till a skewer pierced into the deepest part of the thigh (but not near the bone), shows clear juices and on deep-breasted old breeds that can leave a tinge of pink towards the bottom of a (deliciously juicy) breast. I'm personally comfortable with that particular risk/reward balance.
But store-bought chicken? From an unattributed source? At $1:15/lb? Pass me the probe, please.
Best Answer
If the raw spot was in a thin area, I'd suggest that it was caused by the pan frying method.
A thin spot could leave a gap between the surface of the pan and the meat itself, and so not absorb much heat.
To reduce these indentations, you can mechanically reshape the meat before cooking (e.g. squash down the higher parts).
In addition, or instead, as soon as you start cooking, it's a good idea to use the spatula to briefly press the meat onto the pan's surface. This will flatten the bottom face of the meat and give it uniform contact with the heat.
By the time you turn it over, the meat will have become firm, so you won't be able to fully flatten the second face against the pan, but that's okay as the thin parts will already be mostly cooked and the parts that still need heat will be in contact with the cooking surface.