I think it's important to draw a distinction here. There's actual pretentiousness, which is people deliberately or habitually pretending to be something they're not, for the sake of image and appearances. It could be trying to make yourself out to be more intelligent or educated than you are, more stylish, more in control of your feelings, more independent... anything. A bachelor who writes pages in his journal every night about how lonely he is, but who puts on a front to others of being quite happy on his own, is just as pretentious as the stereotypical teenage philosophy student who thinks he's Sartre because he's read a few entry level books.
But there's also a lot of stuff that's labelled as pretentious, which is actually nothing of the sort. It's just people being their true selves. But if Person A's true self happens to manifest itself in a way that's quite alien to person B, not being able to imagine themselves ever genuinely being that way, figures to themselves, "If I acted like that, I'd have to be faking, and it'd be for a reason, to impress people, or whatever". And so they judge person A as pretentious.
There's also when person A finds subject X to be effortless and instinctive to them, and as yet hasn't realised that this is their own talent - they still sort of assume that everyone can do it, as talented people often do. They might talk about subject X in a way that makes person B feel confused and left behind, but person A doesn't realise this. They assume that B's silence means they disagree, or disapprove of their viewpoint. Person B thinks A is being pretentious, showing off their expertise in order to make them feel inferior.
In both cases, the judgement of pretentiousness has come more from B's inferiority complex, and A is innocent.
I think that because S and N people tend to live in different worlds, in their minds, they can find each other's worlds incomprehensible and therefore ascribe each other's expression of that world to pretension, falsely. Same happens between E's and I's - how often do you hear E's called superficial and pretentious by I's who just can't comprehend that somebody could be SINCERELY that happy to see another person, and that interested in their everyday life?