[thingexplainer]

Regarding your first point, the trouble (at least in this instance) is that this logic doesn't apply when you're looking for Roger Waters and calling everyone in the phone book with his name. Each time someone picks up the phone it probably won't be the person you're looking for, but you certainly had reason to believe they could be.

They didn't find a strange phenomenon and point out it might be ETI, in which case you're right, the hypothesis wouldn't make sense until you had ruled out basically everything else. They made a hypothesis about what ETI would look like, looked for it, and claim to have found things that could fit the bill.