Is it? There's nothing in this disclosure that says they were fishing. It just says they identified the searches. It's entirely conceivable they had referer logs from the Guccifer site showing hits from Google at specific times and subpoenaed all correlated searches. Law enforcement being able to retrieve this kind of information when it's part of a legitimate criminal investigation is good. The worst nightmare is that broad powers get abused but in this case they caught the right guy.