Panspermia would require that life itself was raining down on the terrestrial planets. Precursors would simply indicate there were a lot of strange and complex organic compounds falling on to the surfaces of planets like Earth, Mars and Venus, and were also likely constituents of bodies like Europa and Titan (well, we know Titan is covered in a literal hydrocarbon stew). What this discovery indicates, at the very least, is there was indeed a lot of organic compound in the early solar system and these organic compounds, at least on Earth, led to abiogenesis. Panspermia would advocate abiogenesis happened at some undetermined point further back.
If we find other life in the solar system, such as in Europa's or Ganymede's oceans, and it has DNA or some very close relative, with similar translation and transcription systems as we find in archaea and bacteria on Earth, then that would be a very strong argument that life in the solar system had a common origin. If however, there is no clear relationship between the two populations; say, they use something similar to DNA, but the genetic codes are different (all extant life on Earth uses the same canonical genetic code mapping codons to amino acids, strongly suggested the canonical code evolved prior to the Last Universal Common Ancestor), then we're very likely looking at an example of convergent evolution, and not in fact at two related populations.
