> Where in that article does it say that it's not an arsenic-based life form?
Life on Earth is carbon-based. There are no phosphorous-based lifeforms that we're aware of, so replacing phosphorous with arsenic doesn't make a carbon-based bacterial species into an arsenic-based one.
In fact, it says exactly the opposite. It goes into detail about why it shouldn't be the much of a surprise. (Not that I agree with him.)