This article got me thinking that the author is perhaps confusing introversion with social anxiety.
https://www.yahoo.com/news/16-tweets-introverts-apos-apos-234048603.html
I'm a natural introvert. I think through conversations that never end up happening. I spend less than an hour, total, on the phone each month, and the bulk of my phone time is either scammers or service people that I call. I don't talk to people that I don't already know at the gym, so it's not unusual for an entire two-hour workout to go by without me saying a word. Most of my hobbies involve solitary things (shooting, reloading, fixing the house). I have only a handful of facebook friends and as a rule, I generally don't extend friend requests. I post once every few weeks about my kids, but sometimes go several months without posting anything. I may glance other people's posts but I don't really keep up on anyone. I constantly fear reading something that will make me think less of someone (usually their internal thoughts I think shouldn't be made public). I don't have any close friends and I do social things around 5-6 times a year. I get my energy from being alone and having time to think.
At work, I've trained myself to be a bit of an extrovert. I look people in the eye. I say hello to everyone whose name I remember--often saying hello to a dozen people between my car and my desk. I speak up in meetings. I express my ideas (most of which I've thought through in my alone time.) I don't wait for other people--I goad them along when they are slowing me down. I talk to other people to solve problems quickly (rather than trying to solve them by myself.) I also have to go on 2-3 long walks each day to keep this energy up as it is not natural to me. People that only know me at work are surprised at how solitary I am.