Although it is highly unlikely that we're the only intelligent life in the galaxy, I don't see these supposed 'interstellar visitors' as being probable. Interstellar travel within a period of even hundreds of years is preposterous, assuming our present understanding of the laws of physics is true. The amount of energy required is simply to vast. So only long-term travel is possible, e.g. "Noah's Ark" style craft that support a crew spanning dozens or possibly even hundreds of generations. Does anyone think that aliens would go to all that trouble, and when they arrive, not attempt to establish any level of contact? It's been over 60 years since the supposed Roswell crash. Have aliens just been "hanging around" since that time? Doesn't seem likely at all.
Of course, there are things about the universe we don't know, so I could be full of shit.