
I've experienced similar... as an NTP, my close ISTJ friend and I appear similar on the surface to many other people who meet us together. We were even fooled ourselves for quite a while, thinking that because we shared interests in the same "geeky" stuff, we had more in common than we thought. Especially as he's one of these ISTJ's who defines himself
in opposition to authority and dresses like a hippie, which gives him a far more laid-back appearance on the surface than is true in reality. It took quite a while for the truth to come out about how COMPLETELY different our approaches to those interests are, and our motives for pursuing them, what we get out of them, the parts we like and dislike and all that.
I can nearly completly second that. I myself have a long time friend, I'ld call ISTJ and tho we are fundamentally different there's some connection we share an intrest into the other that is neither of sexual origin

nor really of a worldly origin. Because there's like nothing we could gain from each other, we both have fundamentally different intrests in life, but nevertheless this bond holds.
He's a student of economics and I am a student of engineering and we both find the other field totally boring. He has no real intention to specualte about how things might work, but he has a fundamental want for precision. Though he sucks at physics, if you once got him started to talk about for example the operation of an electrical breaking assistant in a car, he will be not intrested in the whole thing and only talk bad things about it or make fun out of it, until he hears about a thing he doesnt know yet. And then he will start trieing to remember how a thing was again, in this example the one thing he was intrested in, was to think about how the centrifugal force, if a car goes through a curve is applied to the tires.
That particular thing he didnt know and it made him think for the whole evening what the things again were he learnt about that some years ago in class, eventually leading to him speculating a tiny bit about how it could work and eventually leading to him remembering some things from school, he was sure about and he told me about with great self-convience ( tho it was wrong in the end

).
To get him to this point of speculation is like winning the jackpot. Normally he just doesnt talk about things he doesnt know and he doesnt care to get em to know if they dont intrest him. Only once in a while you get him to do what I'm doing on a daily basis, I speculate about a thing of which I dont know how it works and when I have reached an end point, I look the thing up to see how close I got. But I have no reservations to shout out my momentary ideas changing on a minute basis, a thing an intp prolly wont do, until he isnt convinced.
My ISTJ friend is a steady and reliable guy, he meets with a circle of friends I am part of every thursday and goes out to have a drink. Tho we follow a clear routine thats always the same, every thursday, I like it, cause it gives s0ome structure to my own life. Nevertheless I recently regulary started to bombard our little place of refugee with all sorts of arguements, mainly steming from their wish to gamble for money like every night ( and i dont have so much money ). Since I live together with my girlfriend, I watch my money more closely + my health, which means I dont drink so much no more, nor go out with em regulary no more every thursday.
This attitude of mine has led to the fact that I became quite unwanted in their gathering, I am a bit sad about it, it's one of these times again, when I changed but not my environment together with me.
There was a time my ISTJ friend called me the one real friend and reliable friend he had left. I think that changed since I am hanging out more with my girlfriend than him, he probably would call it "entropies priorieties have changed". He can be very military in his demands and got that all or nothing attitude, I tho like too but I dont need to adhere to in every topic.
I hope that one day, when he decides to get his first job and to move out of his parents home, he and me will get closer friends again, but I fear that my out of control entrepeneurial spirit to conquer the world and his sense for structure, reliverance and security wont be compatible for quite some time.