In order for someone to actually be pretentious, there has to be a pretense. Being purposefully non-mainstream doesn't make someone pretentious as much as a more normal individual would like to believe. Hipsters aren't necessarily pretentious, even when they have a pattern of rejecting the mainstream. A hipster might be pretentious if their image is disingenuous (ex. wearing some article they don't actually identify with, pooh-poohing something publicly while appreciating it secretly), but that doesn't have to describe all or most hipsters.
I get called a hipster because I often reject or have no interest in many things that most people consider good on that basis alone. When something becomes mainstream, I like it less because I believe something going from unknown to mainstream is usually a bad sign, and that instinct is almost always right. Breaking Bad was way better until everyone started slobbering over it and chanted "get back to cooking meth bruh", and look how it ended. Such a long way for a ham sandwich. haha