Chicken – Roasted chicken ends up only salty outside

One option to consider to add flavour to a chicken is brining. I've personally never brined a chicken, but everytime I come across mention of it in a foodie blog, forum or elsewhere, it always seems to be considered a good way to impart additional flavour into the meat.

Since writing this answer I've followed Nigella Lawson's recipe for Spiced and Superjuicy Roast Turkey which has resulted in fantastically tasty and moist turkey at Christmas every year, to the point where I won't countenance turkey at Christmas without brining it now. If this translates as well to chicken (which I fully admit I should've tried by now!) then it's well worth the time and effort.

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.