I think Christopher is dead on with this.
This is my hunch. Your friend believes he has a psychic gift. Some might call him a shut eye. From what I'm getting, it doesn't sound like the guy is using any special technique or being dishonest at all. He probably has read a book or two on how to give psychic readings (probably a book by someone else who believes they are psychic) and has had a number of psychic readings himself. He's most likely regurgitating the type of reading that he has received in the past.
To back up what Christopher said about magicians and cold readings Bob Cassidy said this, "(I am) constantly amused by the number of magicians and neophyte mentalists who actually believe that cold reading is simply a matter of spouting out generalized statements like 'I get the impression that while you appear calm and collected on the outside, you are actually very screwed up on the inside, and might have a scar on your left knee or somewhere. You also have a friend with an A in their name.
"This, (I point) out, has nothing to do with cold reading, which is an art based on years of observing and remembering things that people who have day jobs have no time to deal with."
Your friend was probably someone like this:
This lady honestly believes that she can look at someone and guess their star sign based on the traits they exhibit. If she was to give you a reading she would probably be better than 99% of magicians. She doesn't use a system though, she doesn't have a method. She'd use Barnum statements and she would cold read you, but she doesn't know that is what she is doing. She's just trying to use her psychic powers. We know that means she will be guessing and using her intuition a lot but she thinks she is following something more super natural.