If you've removed something, you have taken it away. So, it makes sense that a person who is described as removed is acting emotionally distant, like he or she has been taken away.
You can also use removed to mean being far away in time or space from something else, as in "the house was far removed from the city," or "online dictionaries are far removed from what students had available in my day." And finally, if someone is separated by several steps in descent from you, they are removed, as in little Johnny, your twelfth cousin three times removed from Little Rock.
