ProTip: Every keynote Apple gives review phones to journalists and influencers to review. They can't release the review for one week (usually tuesday of the following week)They weren’t distributing unreleased iPhones to the attendees!?
This is how these events are always done. There's an episode of the Talk Show with John Gruber where special guest Nilay Patel explains the pain of bringing the new iPhone on a plane that same day.
Basically, if they're asked, they're allowed to say "yes, this is the new iPhone" but they're not allowed to openly review the phone. They sometimes will ask (without admitting they have the device) "What questions do you guys have about iPhone 11 Pro?"