This is a good example of what is often called a "fundamental attribution error". We tend to explain what we observe in ourselves or others to that person, their traits and personalities (a bit like you assumed while reading), whereas that behavior is often caused by the situation they're in. This is why research in this area is so helpful.

A very interesting academic ook about this is "The Person and the Situation" by Ross & Nisbett. It's a nice overview of such attribution errors, which we all make. This blog post is a nice illustration of that too, I believe.