Introversion and extraversion are difficult to differentiate on the Internet. Extroverts have far more body language cues that aren't evident through cyberspace. Also obvious about extroverts in real life is their energy push, where introverts can be energy neutral or sink.
I would guess that that would change depending E-type and instinctual variants. I'm an ENTP 4w3 sx/sp ... I do have my moments of outward energy when I stop introspecting and finally act out. The kind of energy and push you're talking about is extremely sx-ish. An Ne dom with an "introverted" E-type .. especially sp's will not exhume the kind of energy output that's typically taken for granted in the MBTI world.
My SO is an ENFP 2w3, but she has a very strong sp/sx stacking, therefore she's not even half as "extroverted" as my 7w8 sx/so ENFP ex.
I have been wondering lately if [MENTION=5494]Amargith[/MENTION] may have a relatively stronger 3 wing than she wants to see in herself.
Given my understanding of three things:
1. 4 desire to be somewhat desiring of more attractive traits in others may be pushing her towards seeing more of the 4w5 than is really there
2. 4 longing to stand out from other 4s may be contributing to her desire to take on a 'balanced wing' as opposed to a dominant wing.
3. Finaly, I've noticed that 4's tend to type themselves based on the weaknesses of a type first before really looking at the strengths [especially if they're already had average levels], as 4's are typically motivated to think of themselves as inherently flawed. 4w5's are the less extroverted versions of 4w3's .. so I wonder if that was another motivation for [MENTION=5494]Amargith[/MENTION] to take the 4w5 when she did.
Edit: And I agree with her sx/so stacking .. I've recently been in touch with an INFJ 4w3 sx/so and she has way more energy than I do when it comes to staying in touch .. It's a moot point .. but I personally as an sx/sp veery rarely connect with a lot of people and socializing when there isn't someone I'm merged with around is a pain in the ass. I don't even want to leave the home if I know I'm going to be stuck in a place/group where I don't have a chance of merging with someone else.