It’s not accurate. The apparent “accuracies” can probably be chalked up to chance—may seem like too much of a coincidence, may feel like it can’t be random… but that’s more because our intuition of what random looks like isn’t correct. A statistician (I can’t remember his name) was interviewed on a podcast. He explained that he can take two groups and ask them to record a series of heads and tails from a coin flip. One group has an actual coin and records the first 100 flips. The other is coinless, and simply makes up a series of a 100 flips, trying to make it look random. He walks out of the room, they make their recordings, and he comes back to look at each series without knowing which is whose. He is always able to point to the actual random pattern—it will have stretches of 14 or so heads in a row, say, where the human-crafted “random” series will never have heads flip much more than say 7 in a row before going back to tails. He explained the actual statistical likelihood of such long strings—it is actually highly probable in flips of 100—but I don’t remember the actual mathematics. Anyway, the experiment highlights how our intuitive expectations of how random events unfold doesn’t necessarily line up to how they actually do. You could, just by random chance, have friends that are only of a certain star sign or two. Add to that factors like potentially uneven birthrates, and people tending to gravitate towards others with apparent similarities (like feeling closer to someone who shares your name, etc., even though it makes no logical difference.), and it seems like there are many more probable and simple explanations than one that depends on the influence of cosmic entities at birth.
I seem to be the inverse of your experience. My sign’s Capricorn. I don’t match its description—in vague descriptions I fit some of the adjectives and not others. In more specific descriptions, it veers farther away from how people describe me and how I’d describe myself. I like the sea-goat, and I like garnets, and I’ve always liked Saturn (even before I knew it was my sign’s planet), so I’m aesthetically pleased with it, but that’s it.
Looking up the star signs of people close to me… My best friend is Gemini, and so are the two roommates I’ve become close friends with this year. My sister is Aries, and my mom is Libra. My best friend growing up, who I’m getting back in touch with after several years of disconnect, is a Leo. I get along wonderfully with all of these people, yet looking up our compatibility online, it appears that we’re not supposed to get along at all. Then, there’s a certain person in my life that I do not get along well with at all. They’re Taurus, a sign with which I am supposed to be very compatible.
Really, I think it’s just random, and sometimes fun coincidences emerge.