Couldn’t it be possible that one of those planets that was “flung out of our solar system” was actually (Thea) flung into Earth, BOOOM and we’ve got a moon?

Exactly, just like the first exoplanets we found were mostly hot Jupiters. It didn’t mean that there were no earth like worlds, we just didn’t have the tools/knowledge to find them. Planet hunting is still in it’s infancy, we will eventually find Earth 2.

Yup, we’ve detected exactly what Kepler is best designed to detect - which are solar systems far different from our own. Its far easier to detect a giant planet that whips around its parent star in short orbits because they’re a larger noticeable dip in light as well as a greater wobble in the star. Earth sized…