Interstellar travel is theoretically possible. If we have advanced far enough to theorize about it, then it's not outside the realm of reason that a hypothetical civilization millennia more advanced than us would be able to develop the technology. The universe is so unfathomably large and the building blocks for life so common there is no way we are the only life in the universe. It just defies logic. In fact I'd bet money we'll find life in our own solar system within our lifetimes.