Is it common to call Americans with the word "fellow"? Or for official business only?
Answer from a Native speaker
It's fairly common. "Fellow" is typically used to refer to someone who has similar interests or is in the same scenario as you are. It's used in more informal settings or even in a joking manner. However, "fellow" can be used in formal settings to make someone seem more friendly or relatable, such as how "fellow" was used in this video. Ex: Hello, my fine fellow! => joking manner Ex: She worked with her fellow classmates to start a recycling program at her school. => similar scenario