My initial conclusion is that we all make initial judgments about behaviors we see in passing. I am sure this is because we need to label and categorize things as human creatures. So when someone is friendly or smiles at you, how do you interpret that? Are they being courteous? Do they want something? Do they like you? Are they "hitting on you"?
Then based on the situation, do you form an opinion about that person and their behavior?
These are all questions we process and internalize individually based on our life experiences. I realize the environment we are familiar with must effect the way we perceive these things tremendously. It made me reflect and compare how 20 or 30 years ago people "greeted" each other more frequently, nodding, smiling even saying; "How are you today?" I believe today we are more cautious, detached, and become suspicious when we perceive someone is "overtly friendly", thus we categorize or label them. This may be a reason our self perception may differ from others perception of us, especially as times change.