tl;dr : just read the bolded portions
My theory: extroverts who are victims of bullying, who suffer forced isolation/exclusion, and who are coping with emotional baggage may mistype as introverts. What do you think?
Evidence: Nothing "scientific", just my own observations/person anecdotes (go Ne!). My father was an interesting individual. It's a long story, but he kept my family rather isolated and prevented us from forming close relationships with outsiders. We also moved around a lot. Both my brother and I were raised more adultly and grew accustomed to entertaining ourselves. I'm an ENFP and while I cannot be certain of my older brother's type, I'm guessing he's an ENTP. Neither of us fit in well at school (being the new kid sucks) until late middle school/early high school.
He became very rebellious during high school, embracing newfound friends, questioning my father, and became bitter and reactive. He was still very surprised when father revealed all of his lies and left my family. after that, he withdrew from his many friends and now has few close ones.
I was a typical Ne child, full of energy and ideas and playing pretend. I was loud and friendly, despite my learned caution. Note, I am a 4, so I remember feeling very ashamed from a young age, but it did not hamper my natural enthusiasm. Very 4w3, then. My Fi came on strong soon after, 'round 7 maybe, and that's when I started getting causes. I am an ENFP. No doubt about it, Te-bitchslap from 13 onward. But from age 8 up, I was bullied and excluded. My home life interfered with preserving connections as I switched to different schools in the same area, and I failed to make friends and satisfy my need for social connections. After my dad left, I moved to a better school, and made friends, but it felt like relearning how to swim, terribly awkward. Even now, when I move to a new place, my default setting is LONER. I act really cold and prickly.
Why it matters: If you mistype as an introvert, and the rest of the description seems kosher, you'll ignore your need to belong even more, especially for xxFPs, who are chameleons anyway.
Not sure where I was going with this, but it's the beginning of the start of an idea.