Indian tandoori chicken is cooked in a tandoor oven, with heat reaching 900F. How come the chicken does not dry out? Because of the yogurt marinade?
If you see this recipe https://www.youtube.com/watch?v=F9Fzpi99tlk - When cooked in oven he is using two deck plates. Chicken is on top and underneath there is some water. I agree that Tandoor cooked in conventional oven without water plate will be very dry.
The chicken stay moist because it cooks quickly (very high temperature); it does not have the time to dry out.
I would imagine that the cook time must be controlled because it can over-cook very quickly.
The yogurt marinade will impart some flavor and help tenderize the meat.