Panspermia is a recent scientific hypothesis, but not really new. The term has been around for thousands of years. The cometary hypothesis is not all that new an idea either, but even so, the comets and asteroids etc are all from the same region of the universe, that is, inside the solar system and would probably have some common characteristics with each other and earth whether they collide or not if the nebular hypothesis of planetary origin is at all valid.
“inside the solar system”
If you mean within the orbits of the planets, that is not correct. Even if you mean as far away as the ends of the Oort Cloud which extends out about 2 light years and contains about 1 trillion cometary objects, that still may not be correct. See my comment #74 for an interesting source. Some comets may come in from outside the Oort Cloud.