I think another way to word the question is that if they're so confident with the technology, why didn't they demo it live? Why the recording? And why clearly edited recordings?
I wouldn't trust a live demo in that situation even without the AI in the mix. You have thousands of people in the room and millions online and you get "Hold please" when calling a business. Great demo.
Steve Jobs famously called Starbucks to order 4,000 lattes during the original iPhone launch.
"Dear aunt let's set so double the killer delete select all", et al. In other words, a demo is supposed to be awesome...actually running the real thing tends to crash and burn spectacularly. What the uproar seems to be about is that Google insinuates "this is not scripted" (doesn't quite claim it, it's extremely carefully worded: "Google Assistant actually calling a real salon" - never claims it is not rehearsed, just that it's a phone call and a hair salon), while showing something that almost sounds non-fake. Almost almost.