They may be lying. If there's a gag order, they may be required to lie. Or they may consider "review" not to necessarily be human review. Or the person writing that may simply not know. We don't know what's going on at google, and with no transparency, it's hard to have a lot of trust, particularly since there are many examples of government overreach in the past.
Sure, google and facebook and whatever should push back, but it's clear that if the government really wants to abuse its power, they won't stop it. Given the current witch-hunt on whistleblowers, it's clear that those in power do not appreciate being questioned. Trust is fine, but verification is better.
Actual transparency, not just words? That could be free access to their internal architecture (not exactly likely), or more plausible, external, independent auditors.
However, I think you're focusing on the wrong party here - I think it's a lot more reasonable to request this of the government than of companies. There's no reason not to require the government to publish the general structure of what they're doing in great detail, and to let others make up their own mind if it's overstepping its bounds.
In short: I want an independent parties to have free access and be allowed to verify what's going on.
Sure, google and facebook and whatever should push back, but it's clear that if the government really wants to abuse its power, they won't stop it. Given the current witch-hunt on whistleblowers, it's clear that those in power do not appreciate being questioned. Trust is fine, but verification is better.