I don't know how BGP works in detail, but I have to wonder how HE would be able to observe peering between Google Fiber (AS16591) and Google (AS15169). Google Fiber won't carry third-party traffic through AS16591 to AS15169, and vice versa, so I wouldn't expect either AS to announce routes that would expose the peering. But they are definitely peered, as confirmed by a simple traceroute.