I think it is not that far fetched and a more valid theory than complex life appearing from nothing.
We know some eggs, embryos and sperm/pollen can be frozen indefinitely.
It’s possible to have a planetary impact so massive that rocks with life deep in their crevices are ejected into orbit and flash frozen in space. These rocks can then travel for millions of years with the center in a cryogenic state and protected from radiation.
If the rock happens to fall on a suitable planet one day, life can thaw, exit the crevices and live on.
I think we are far from alone and the Universe is big game of cosmic billiards far beyond the scale of any human. In our very limited lifetime here, most of us don’t even get to see one “ball” so it seems far fetched. But over millions of years, there have been many rocks that arrived from very distant places.
There has to be a start somewhere. The Comet theory just moves the issue of where life started off Earth somewhere and makes the issue of how life began even harder to unravel.
Life is essentially self replicating information. Given that definition we've already seen the birth of life here on Earth: the Computer Virus. It was not meant to be a form of life , it was an accidental side effect of devious programmers. Imagine it, a silicon based form of life that lives on electricity! Good thing it has not become as adept as other living things (so far!).
The point is you can never know in advance all the clever ways nature will create life.