I'm not the first nor the last person to say this, given the fact we're 24 threads deep and the same questions pop up constantly but not all dogs bark at strangers. It's entirely possible that the dog is used to numerous people coming and going and being around commotion at all hours of the night due to the house being a known party house.
I have a 2 year old Boxer who is quite large for his breed (and he's not fixed, so he can be quite excitable), yet rarely ever barks even when a stranger is at the door. He's actually a horrible guard dog that it makes me laugh often.
Given Murphy's breed, the circumstances of where the dog has lived for most of it's life, it's young age, it's own unique personality, I dont think anyone could say whether it's weird if the dog barks or not. Hell.. it COULD have barked, yelped or growled yet it roused no suspicion because for all we know that was the norm for Murphy?