What are the odds that we would find anyone this way?
Well, what are the best case scenarios for this?
1. aliens aren't looking for us but aren't actively hiding from us
2. use radio technology or something equally noisy that would pollute space at light speed
3. have actually visited the Sol system and left some physical evidence for us to find
1. Seems really naive, but since it's mostly what we're doing, I have to rate it possible.
But this seems like it would be the purest luck to have an accidental encounter or discovery. The galaxy is really old but its also really big. The odds of an encounter here seem really small.
And of course, this assumes it didn't already happen. There's lots of old stories of men from the sky we dismiss as mythology, or build slightly more advanced belief systems on.
And lots of new stories of unexplained things in the sky. And even though these are often made by military pilots known to be sober individuals with great eyesight, they are dismissed.
2. Well this either requires a culture at about our technology level within 100 light years, or would require more sheer luck.
Unless the culture is so close we detect each other simultaneously, with us puzzling over the Gurignagh Show and them puzzling over I Dream of Jeannie, it requires something like SETI. Assuming they detected us that (not a sure thing), then any dedicated signal would a LONG time to get here.
Again at the best case scenario, a culture 100 light years away immediately detecting our earliest radio signal and immediately sending a response, that would just be getting in now, assuming we understand it when it gets here.
For example, scientists see unexplained flashes of light in the sky on occasion but know so little about the galaxy that they attempt to explain these as natural phenomenon.
3. This one is probably our best bet, finding some alien trash but it runs into two problems as I see it. First, space is BIG.
But this is best-case scenario time, so let's assume that somewhere in our very solar system is an alien garbage heap of stuff they left while passing through, let's say 100 years ago (best case remember).
How much of our solar system has been explored? We've sent a few robots to Mars, some some satellite mapping of Venus, and done some flybys at 1,000 mph of the rest.
Now imagine Earth is uninhabited and you're looking for a 100 year old trash heap from orbit. Would you find it? Maybe- eventually.
In short, before we can write off #3, we have to do a LOT more exploration of our very local space.