PeterJ isn't an established user:
But on the review page he suddenly is:
Why is that?
Also: on the review page we see images of the latest reviewers. Established users don't have shadow right there:
This appears to be intended. The usercard is different, on the review page it appears for everyone and only shows only the user's review activity (for all users, not just sub-1k), not the full expanded profile. Compare:
On the review activity:
On the rest of the site:
To clarify, that isn't the Expanded Hover Card that Established Users get, it's much more in line with the basic card that everyone has. The avatar list for each review queue is to show who is actively reviewing, so only the avatar is shown by default.
The Expanded Hover Card is only available for question and answer posts. You'll notice that you still can't see an Expanded Hover Card on Non-Established Users question and answer posts.