Assuming gets you nowhere...
Don't get me wrong... I love to people watch, however, along with people watching comes assumptions. Those assumptions are probably a good 70-85% incorrect most of the time.
One thing in graduate school that we studied was interpersonal communications, the interactions between two people. This included verbal communications in the form of words, but not only that, also the non verbal cues that went along with that communication and also the way things are said, not just the actual words.
Considering I studied these cues for a few years and have read a significant number of scientific studies related to this work, I still find myself interpreting people inaccurately at times, which leads me to believe others most likely do the same in many situations.
Look at the faces below.... assume what you wish... but that doesn't mean it is really what they are trying to portray or how they are actually feeling.
This little kid looks like he is having the time of his life. We assume he is happy as ever. That is probably an accurate assumption but never 100% for sure.
Our Favorite Man Men Character here looks cool calm and collected - but he is kind of hard to read, he could be angry, tired, focused, interested in something he is looking at, bored, this can be easily mistaken for something else without investigating further...
Look at this chick.... one would think it's quite evident that she is devastated/sad over something. But put that face in a different setting, say, a wedding, and she could be showing happy tears. You just never know, that's the point.
Never Assume Anything.... take the extra steps to ask and find out.