Based on my results, I wondered if it's based on how many I/me/my statements you make. The two stories I got extrovert for were heavy on I/me/my constructions. The pages coming out as introvert were not.
If it is how they do it, it'd be easy to bias. A diary blog would tend to come across as extroverted and a article blog as introverted. The same person could write both.
Actually, I'd have thought it the other way around, the "me" pages as introverted and the factual pages as extroverted. As it happens, the first page of my blog is not so much about me; it's mostly an obituary for someone else, and so I tried a page form my website which is more about myself, and that too came out with an E: ESTP, the Doers, like the post above, which is absolutely and completely not me:
"...often full of energy, talking, joking and engaging in physical out-door activities.
(NOT!)
... They might be very impulsive and more keen on starting something new than following it through. They might have a problem with sitting still or remaining inactive for any period of time.
(NOT! I love sitting still; I love meditation and everything quiet and contemplative.)
"
So, this site definitely brought out a fail with me.