Sounded like BS. Looks like BS.
Eh. I agree with bigblueinsanity -- even if this particular story appears fishy (and it does), this is all but inevitable and sentient AI may already be here and the powers that be are slow rolling the information out like they're doing with UFOs.
I posted this in GYERO but a sentient supercomputer makes an appearance in in Jack Carr's newest novel that is very, very similar to what the Google engineer is describing. Jack Carr is a former Navy SEAL and, as such, I believe he has to get his novels approved by the Department of Defense before publishing them. It stands to reason that if the DOD wanted to keep the technology under wraps, they wouldn't let that appear in the novel.
In both the novel and the Google engineer's statement, the AI appears to refuse payment for its services as unnecessary, which is an odd and specific fact to see in two dramatically different settings.
We are going to require some form of advanced AI or supercomputing to handle the threat of hypersonic missiles because an incoming hypersonic moves faster than the speed of human comprehension and you can't have the decision to react to require a human in the decision loop.
The future is now, I guess, and given the way the 2020s have gone an emo supercomputer drowning in its feelings being the most intelligent sentient being on Earth would be pretty much on brand for the current state of world affairs.