4 arguments
First there's the article.
Then I've read something similar in a french astronomy magazine.
Then, the claim of extraterrestrial life is as Carl Sagan said an extraordinary one and it requires extraordinary proof.
Every time we think we know something about space, it surprises us...Yes, but it can also often disappoint us (nor Mars nor Venus, nor the Moon are like culture had tought us before we went there for real).
The point is: if we're looking for life and only that, then we'll be disappointed. But if we keep an open mind and accept whatever there is, then we'll be surprised!