Alien Life in the Stratosphere

Scientists in the UK have recently made the claim that they have found alien life in the stratosphere. the specimen to which they refer is a diatom. Found at between 22 and 27 kilometers above the surface of the Earth, their assertion that that there is no discernible means by which an organism of such a size could have been lofted into the atmosphere from the surface of the Earth, and therefore must have come from space. The allegation as that, such an organism could have made it to such an altitude by being blown into the upper atmosphere in a volcano, which did not happen in the three years prior to the discovery of the organism. One possibility that has not been discussed is whether or not the specimen could have been lofted into orbit 65 million years ago when the Earth was purportedly hit by a large asteroid, somewhere near the Yucatan Peninsula. Is it not possible that diatoms of this nature could have actually been lofted into orbit and left in interplanetary space for millions of years, and that these organisms, left in an orbit around the sun as part of a debris field from the asteroid impact, eventually find their way back to Earth? Why would this not be a possibility?