I just recently discovered that I am an ENTP rather than an INTP. And it totally makes sense. I have all the hallmarks of an ENTP: fickle, extremely excitable, lively imagination and talkative. Does anyone know why its so easy for ENTP's to confuse themselves as INTP? I think there might be something in typology theory that I don't know about yet.
The tests are bad, as ID and others have repeatedly pointed out.
And yes, as AUM pointed out, Ne as an extroverted function is stimulated by ideas and possibilities, as opposed to 'people', and these are readily available in the form of books, movies, music, taking courses, and indeed, the internet, making the Ne-dom seem quite introverted indeed.
(Although nothing will kick Ne into high gear than a discussion with a fellow intuitive, cause of the feedback that stems from that in the moment. You throw out an idea, you get one back, you toss one back, you receive another.. like a rapid game of intuitive table tennis.)
But I believe there is more to the story than that.
In the case of Ne-doms specifically, it is our natural inclination to shift through different ideas, to come up with multiple interpretations and, when it comes to testing, to try on different roles. We're open-ended, always ready to take in additional information to shift our internal frameworks. We're multi-faceted, always ready to adept to the external world. That makes it easy for us to mistype, and rather hard to settle on any given type.
But that merely answers half of the question.
Now why do ENTPs mistype as INTPs specifically?
The reason for that probably has to do with the fact that your dominant function is somewhat 'unconscious', in the sense that it is akin to water in a fish tank that the fish swims in, or the operating system of a computer. It is so normal for you to be that way, that you're not really aware of the OS, you're aware of the Apps you run on it. The Apps are then Ti, and to a lesser extend Fe.
Additionally, think of what you're doing when you're taking a test or even 'just' thinking of the self: introspection. How do you introspect? Through your introverted functions. That would be Ti. So you even 'tune into' Ti at that moment.
So Ne being what it is, and being unconscious and adapt at Ne, conscious and rather adapt at Ti, tuning into Ti to take tests, and adding in to that the fact that Ne as an extroverted function is energized by 'potential' and 'ideas', you have a perfect shitstorm to lead you to the exact wrong conclusion of INTP.