Back before they started blurring the lines between AS and HFA, a narrow interest for an Aspie was described as:
1. something that demands an extraordinary amount of the individual's time, thoughts and energy
2. a source of stress or frustration if the individual is not allowed to pursue it, but the individual could voluntarily pull themselves away from it if asked (unlike an OCD obsession)
3. something in which the individual was unusually motivated to become proficient at, very knowledgeable about or an expert in, rather than something they simply enjoy a lot--I remember this was why AS used to be nicknamed the "little professor syndrome" because we as kids would have tons of info about our interest memorized and could recite by rote. like we were giving people a lecture
4. due to this level of expertise, it that could provide the individual a means of employment or social acceptance down the line, despite social deficits
5. could be anything, but often times the interest seems narrow or unusual to others. Most frequently it is an interest in something involving systems or systematic or scientific thinking, i.e math, computers, transportation. One of my Aspie interest as a kid was horses--typical of Aspie girls--but unlike other girls who loved how pretty horses were, I was far more interested in knowing all the breeds and how they differed and where the came from, horse anatomy, horse genetics, horse evolution. I was far more scientific in my interest in horses than your typical girl
That's how it was defined when I was dx'd back in the late 90's. Now it seems like it's just anything that you are obsessed with, even if it's just a escapist activity, like indulging in anime or video games so to avoid the real world.
But my griping and complaining aside--yes, an Aspie interest could be something that could help you socialize and create social opportunities. Throughout university I relied on my Aspie interests in music, literature, philosophy and theology to not only socialize but get employment. I couldn't talk to people for the first few years of university unless it was about one of my Aspie interest. All my jobs that I had back hen stemmed from my Aspie interests. But now I don't live somewhere where that sort of knowledge is considerable very important and I struggle to find work and I never socialize with anyone anymore, except online.