my original comment was an easy joke
Ah, I thought you were serious.
But yeah, I buy that argument. Moreover, I don't think they just achieved interstellar travel. I think, statistically, they're probably millions of years ahead of us. If the Singularity is countable infinity, they're approaching uncountable infinity. Statistically, I think they're out there.
that simply haven't occurred to us
I agree. As the Doorknob said to Alice, nothing's impossible.