The important thing to remember is that we're dealing with very sparse sampling of a large population of comets that are the survivors of the early solar system. So while this result lowers the plausibility of the proposition "Earth's water came from early cometary impacts" only a liar or a "science journalist" (but I repeat myself) would claim something completely and utterly false, like, "Scientists prove Earth's water not from comets!" Yet that is a headline I've actually seen on these results.

It's an interesting finding, but Jovian comets are one population of survivors. We have a lot more data to gather to fill out the most plausible picture of the early solar system and the likely source of terrestrial water.