All i could think of was: "damn it, all that organic material we found on other planets might have come from earth instead of those planets developing life" we might be alone after all :( (at least in the near vicinity)
It also raises another possibility not mentioned in the article, which is that life is in fact rare, the only life anywhere near us is what developed on Earth, and discovering life on Mars or the other possibly-hospitable locations in the solar system may not prove that life is common if it can be shown to have derived directly from Earth life.
If that life uses DNA, centuries from now the kind of genetic analysis we use to determine where one species branched of from another could be used to find where life on one planet came from.