It is unclear how the publication managed to come by a Pixel 4a so early, and neither publication touches on its origin apart from resurfacing the original hands on video back in March. But it looks pretty clear that is a genuine phone, albeit a pre-release model.
Apparent retail units of the Pixel 4 leaked a few weeks before its launch back in September and were unboxed and reviewed on YouTube in the same way.
Google seems to have a pretty leak friendly supply chain. The devices normally leak extensively pre-launch, and are then even reviewed online with video and images as has happened with the 4 and 4a. The Pixel 3 XL was found for sale days before its launch by Engadget, who posted a whole hands-on video.