Let's just play this safe and assume that, until more samples have been collected and detailed DNA analysis has been done, the real answer to the question, "Is bacteria found in Antarctica's Lake Vostok actually new to science or just contamination from the drilling?" is "We don't really know." This is a great example of why making scientific pronouncements from the field, before you've had time to do the really in-depth analysis that goes into writing a peer-reviewed research paper, can be problematic. Right now, you've got different camps of researchers making totally contradictory claims. Who is right is, so far, anybody's guess.
"You can say anything you want in a press release". Sadly, that sentiment is too true. Turns out, recent reports of the discovery of previously unknown bacteria in samples hauled up from the waters of Antarctica's frozen Lake Vostok have turned out to be premature. The bacteria turned out to be contaminants carried by the drilling and collection apparatus. At Scientific American, Elizabeth Howell talks about this flub in the context of other stories where scientists bypassed peer review and announced findings to the newspapers first.