I'm surprised by the strong objection. I understand that the lead scientist is with the NASA Astrobiology Institute, but I still think that despite the important implications for astrobiology, calling it astrobiology is questionable. If neither NASA nor any astrobiologists had been involved, exactly the same results could have been obtained, and the astrobiology connection (though it might be played up because it is an interesting angle) would more clearly be incidental. In other words, I don't think you lose any accuracy or diminish the finding by referring to it as biological rather than astrobiological.
That said, I'm not sure I really want to get caught up on "biology" versus "astrobiology" as terms. I think the greater point (or at least the point I was trying to make) is about communicating clearly and managing expectations. When you say astrobiology or exobiology, invariably some people are going to cry, "What, no aliens? You tricked me!" If that indignance prevents them from trying to understand the importance of the story, should we even bother trying to cater to them? I don't have a good answer for that. Without raising the idea of extraterrestrial life, they might not have been engaged at all. It's just something for those involved in public outreach to be aware of.
I guess I tend towards thinking of astrobiology as the subset of biology dealing with life beyond Earth--a convenient and arbitrary definition, perhaps. In any case, under this definition, with no validated extraterrestrial life, astrobiology would be a largely theoretical science or a line of philosophical inquiry. But if that's too narrow an interpretation, maybe this indeed is an example of experimental astrobiology. Hence, I may have overstated my position when I said this is not astrobiology.
At this point, however, I fear I'm drawn towards philosophical digression. It seems the motivation of the scientist comes into play because she could end up with the same results whether she is a) looking for insight into how life could exist elsewhere in the universe or b) studying life in extreme conditions on Earth. The impetus and interpretation become the categorizers (in practice, I don't think it's too cynical to link this to funding source). On the broader question, I should perhaps defer to the epistemologists--does the nature of knowledge change depending on why it was sought or what is made of it?
Back to the question, what would I consider astrobiology? Well, if life or its precursors were found on Mars or a comet, that might work for me. But what happens when it falls to Earth? I don't know; I've never been particularly comfortable with the blurry divisions between disciplines anyway, so if I consider the dividing line between, for example, psychology and sociology to be tenuous, how am I supposed to feel in this instance? The thing is, knowing what to call it doesn't really affect our ability to understand or use it, it just changes the way we talk about it--which may be important, I grant. But this brings me back to the communication aspect. And as far as that goes, I feel like I've gone through a lot of words without saying much. Therefore, let me summarize like so: I understand why they call this astrobiology; I probably wouldn't call it that myself; most importantly, I think many people will be expecting something else.
That said, I'm not sure I really want to get caught up on "biology" versus "astrobiology" as terms. I think the greater point (or at least the point I was trying to make) is about communicating clearly and managing expectations. When you say astrobiology or exobiology, invariably some people are going to cry, "What, no aliens? You tricked me!" If that indignance prevents them from trying to understand the importance of the story, should we even bother trying to cater to them? I don't have a good answer for that. Without raising the idea of extraterrestrial life, they might not have been engaged at all. It's just something for those involved in public outreach to be aware of.