It's only speculation at this point but it's one I've harbored for many years. Part of this is because of how common we've found organic materials to be in the universe, and part of it comes from how poorly other geocentric ideas have fared.
If you want to assume it came from somewhere else, you either have to invoke some kind of magic, or assume it happened somewhat along the lines that it would have done on Earth, then arrived somehow. It just kicks the can down the road without solving anything, IMO.
Panspermia is an attempt to explain one inconsistency in our observations so far: it appears that life spontaneously emerging from inorganics is hugely unlikely. On other hand, geological records show that life appeared on Earth very soon after it became viable.
If life on Earth originated somewhere else, then this discrepancy can be made to disappear. For example, abiogenesis only needs to arise once within a large radius around Earth and within a much broader time margin. Hence it can be a very rare event while still not making early life on Earth a unique event in the universe.
I don't personally believe panspermia is likely. But it is a valid theory (although without much supporting evidence as far as I know).
With a sample size of 1, and loose record-keeping from ~4B years ago, it's hard to tell, but we don't really know if it took life 1 day or 500M years to evolve once it was chemically/geologically viable. We do know that life was very primitive for > 1B years (not even eukaryotic, let alone multicellular).
We also know that space isn't teaming with little biologically active spores from other worlds (unless it is and the government is covering it up, of course), which suggests that in the vastness of space, life doesn't really hitch rides on asteroids or comets and colonize the galaxy accidentally. And if some beings were doing this on purpose, why not send more advanced life forms or robots?
Cf. https://en.wikipedia.org/wiki/Tersicoccus_phoenicis "It has only been found in two spacecraft assembly clean room facilities..."
Maybe it's not T. phoenicis but it's not ET.
(However, if it somehow turns out to be alien, that seems to be to imply that interstellar space must be swarming with bacteria, yes? For the ISS to have encountered some already?)
The error of course is that the stars are really unimaginably far away and hence there is parallax but it's practically indiscernible. The Greeks thought the stars being that far away was the less likely answer to the apparent lack of parallax than the Earth simply being the center of the solar system.