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I really don't see any reference in the article to consideration of the possibility that these meteors might be terrestrial in origin - blasted into space from Earth's crust by a large impactor, and eventually re-entering, to be discovered and found bearing remnants of terrestrial bacteria.
Nothing in the paper is inconsistent with that hypothesis. All of the attention in the article devoted to possible sources in comets, asteroids, Jovian moons, and the Kuiper Belt, but no consideration given to the closest source of organic materials - the earth itself.
Sounds like a severe case of confirmation bias...
The deuterium/hydrogen ratios are consistent with cometary origin