The actual article's conclusion is basically "for there to be life on Titan, there needs to be more carbon in the ocean than would be transferred solely by surface impactors". It absolutely does not rule out the existence of those carbon source.
> It is unlikely that the calculated fluxes are sufficient to maintain a detectable biosphere, unless the thickness of organics on Titan’s surface is greater than currently estimated, abundant biomolecules are available from Titan’s rocky core, or surface biomolecules can be delivered to the ocean by a process other than impact. Our calculations suggest that despite Titan being the most organic-rich ocean world in the Solar System, this does not automatically imply an organic-rich and habitable ocean.
With GPT, at least the writing quality would be better.
https://en.wikipedia.org/wiki/Titan_(moon)#/media/File:Titan...
https://www.planetary.org/space-images/interiors-of-icy-bodi...
There were plenty of opportunities for compounds in the rocky center of the moon to get mixed into its ocean.