Was it Io or some other moon they said had strong evidence of hydrocarbons?
Methane is one of the building blocks of the early solar system, it is very abundant int he gas giants, it wouldn’t suprise me if there were large amounts of it on earthy earth that have been compressed into hydrocarbons.
Only Coal has been proven to have been made from plant matter due to fossils of plants and Forrest animals being found in coal, plus we see peat , then soft coal and then hard coal or anthracite. We see natural gas and light crude and heavy crude. But little if any fossils in oil. It could be the shallow oil deposits are from fossils, but the deeper ones could be abiogenic.
Saturn’s moon Titan has a methane atmosphere, tar like continents, and seas of a kerosene like liquid.