The ENTP wants to be out and about with his friends on Friday night. The INTP wants nothing to do with the public - especially on a busy Friday night.
Even if the ENTP's Ne is underdeveloped and the INTP's Ne is well developed, I think the difference is still that one is drawn to people, while the other is drawn to the inner world. It's hard for me to even imagine an ENTP, however, with an underdeveloped Ne. If they are a true ENTP, then Ne is their primary function. In other words, it's what they do best and where they most naturally operate - without even trying, that's just what ENTP's do.
I can't imagine someone like myself, an INTP, with an "underdeveloped" Ti.
Perhaps the person in question is xNTP? I have a relative who fits into this category. Very ENTP in some senses - successful entrepreneur, large network of friends/associates, loves to give motivational speeches/be a guest speaker at seminars in her field of expertise, enjoys hosting parties, but................
Also withdraws for long periods of time - the whole "locking herself in a cave for a week" thing, really gets worn out by people and their problems, has a much bigger collection of books than I do, and generally has no problem being a complete homebody.
With her, it's a back and forth thing. One week she's out and about, making things happen, traveling, dinner with friends, and seems like she can keep going forever.
The next week it's as if she's crashed and burned. In her slippers and robe at 1pm on a Wednesday, not returning phone calls, and lost in books.