A lot of people will incorrectly interpret their dog's reaction to certain cues and conclude, "My dog is racist," or, "My dog hates the mailman."
What typically happens is that the mailman, meter reader, etc. will approach the residence. The dog barks, the mailman delivers the mail, then moves on. While the mailman is just going to his next delivery, the dog interprets this as having prompted the mailman's retreat by barking. It gets reinforced daily (in the case of the mailman) or monthly (in the case of the meter reader). I would wager that your neighbor's Airedale may hve barked at you early on, but never succeeded in forcing you to retreat from your property, and as he grew accustomed to you, and familiar with you, never saw the need to challenge you as you approached.
All I know is that I witnessed more than one meter reader VAULTING the the side fence into my yard with “Ben” in hot pursuit.
Mostly my boys took care of that dog, but one day my daughter had to cover for her little brother who was away at camp. I was inside and I heard a distant wailing coming from outside.
“Mom, mom, help.” There was my daughter pinned at the back door with big, ole Ben standing in front of her with his front paws on her shoulders.
She was upset because she was on her way to work and Ben had rubbed his muddy paws all over her white pants. She had to change and might be late.
Ben wasn’t going to tear her throat out. Just wanted to say hello. But that was not the way he went after the ENTX men.
I meant to add that people will smell different depending on their diet. I think that dogs pick up to that. Back to the Afghan dogs — the Muslim diet would be quite different from that of the soldiers and the Marines. If dogs can detect diabetes, epilepsy, and cancer with their noses, I have no doubt that they can tell the difference between someone who ets MREs and someone who consumes a traditional Middle Eastern diet.
I know from personal experience that dogs can detect fear and will go after someone who exudes fear. They will leave someone who is comfortable with dogs alone.