If you look into the scientific research on the subject of how biological matter can and is found to be preserved for fantastically long periods of time, you will have the opportunity to be more surprised and less boggled. Exobiology is finding extremely difficult to sanitize Terrestrial space probes to avoid contaminating extraterrestrial venues.
So it happens all the time, is that what you’re saying? It’s so common one shouldn’t be surprised? It’s as common as three-headed cattle, honest democrats, teenagers showing gratitude and benign muslims?
Or do you mean, since it’s remotely possible one shouldn’t find it surprising that it occurred? I’m sorry but, yes it’s possible but it doesn’t happen much, therefore, I’m surprised.
When it arrives....
"Look, Vardig, these creatures come from a sterile world! Quick! sneeze on it and send it back!
They'll all die and their world will be ours without so much as an orbital bombardment!"