It's my opinion that the "proper temperature" is a number set by lawyers, not by chefs. The government standard for a roast bird is 180°F (83°C)! Are you kidding me? HTST pasteurization is 161°F (72°C) for 20 seconds, but my turkey has to get to 180°F for safe human consumtion? What the hell kind of bacteria do they think live in there?
165°F (74°C) is a common number, and a pretty decent one, though I always take mine out before that for the reason below.
You need to remember that the internal temperature of the bird will continue to rise for a while after you take it out of the oven: the heat on the outside is still migrating inward. If you wait to take it out until the internal temperature is the "right" temperature, by the time it peaks, it'll be 10°F (~5°C) HIGHER than the right temperature, and that's in the dry zone. We're talking 190°F (88°C) thanksgiving football. Blech.
Dark meat almost always handles being overcooked better than lighter meat. The breast is the hardest part of the turkey to cook correctly. If you haggle with the temperature, and your white meat is still on the dry side, you might try brining the bird for 24 hours or so. It makes a big difference in terms of juiciness.
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.
Best Answer
You are probably touching the bone with the probe tip