Well, I guess I need to know what a "clear chamber device" is as opposed to a traditional flag. I've never shot at ranges where it was required (LE range, just needed open action and standard safety controls).
It looked pretty obvious to me that the action was open and safe from 15' away. It was a bright orange magazine shaped plug that (appeared to be) locked in to the mag well. He had a red "unloaded" or "safe" fabric flag flying on the bottom.
No matter. Just curious. I thought the SO's did a good job of keeping everyone safe.