ok so why are people always surprised when I am a pretty good public speaker?

Is it just like, public speaking is hard or is it something specific about me that makes people think I would be bad at it or not well spoken? Everyone is always surprised that I am a good speaker. I think it is probably because I am shy or quiet. So people assume that I would dread public speaking. 

Anyway I did a presentation in class today and like 3 people came up later and were like OMG THAT WAS AWESOME and I guess it’s because I’m quiet in class?

FYI I am a good public speaker I don’t really get nervous about it or whatever.

edit b/c someone specifically said, “Wow you are really well spoken!”