Considering the amount of time life has had on this little mote to figure a way off it, who’s to say it hasn’t? And what would be the method?

Well, thanks to Earth’s magnetosphere, there is a more benign method of launch than being nearly struck by a 40,000 mph chunk of asteroid.

Foreground is Surveyor 3. The Intrepid is seen in the background.
Photo Credit: Photograph taken by Apollo 12 Lunar Module (the Intrepid) pilot Alan Bean.

The microbes retrieved from Surveyor 3 during Apollo 12’s visit were Earthbound creatures that survive relatively well at sea level conditions. On the Moon, they survived in dormancy for a number of years. Microbes that exist in the upper reaches of the Earth’s atmosphere, living a cycle that might carry them far out along the plasma sheet of the magnetotail, are more likely to survive the very-near vacuum conditions in a non-dormant state -- and more likely to break free of the magnetosphere to open space.

Well who is to say the spores did not originate on the only planet in the region thus far proven to harbor life?

I think we’re jumping the gun by decades here.

We'll first need to:
* check any spores for compatibility/similarity with Earth spores
* see what's available on other planets (do similar comparison if applicable)
* map currents in the Solar wind that would bolster/refute a "from Earth"/"from local life-harboring planet/moon/asteroid/comet" theory

Until we can crack physically the heliopause itself and take a hard sample of interstellar space, any life found in space would have to be local, and considered a kind of domestic breed.

Dan