The petapixel article with the photo in question says an Apple tech said Apple is beta-testing a feature that chooses the best picture from several taken. Does Apple roll out beta features to a subset of users like that?
No; it's explicitly opt-in, you have to go out of your way to install beta versions of iOS.
The example does feel “too clean”.
Has anyone at all been able to reproduce something similar?
iPhone sensor still raster-reads so I would have expected more motion between these three poses in that time span. I feel by the pose and image quality, there was more time in between