I think the theory is that adding the pressure cooker aspect ensures the chicken is cooked quicker and more safely (pasteurisation) and is juicier as "drying out" is greatly reduced.
I understand the fast food concept of broasting but juicier ? To me anything fried in oil tastes more of the oil rather than the meat juices.
I'm not really an expert however - I haven't eaten a fast food takeaway in decades.