This is my opinion but based on the connotations of the words I would say that an observation is the information you gather from something indirectly, like you're not asking someone a specific question. For example, if I see that someone eats everything on their plate except their carrots, i can observe that they do not like carrots. However, an interview would be directly asking a question for an answer. I do not have to watch someone not eat the carrots on their plate to know they don't like carrots because I will ask instead.