Gas water heater vent device

Wondering what this device is on a natural gas water heater vent pipe. Seller says its a barometric damper, but doesn’t look like it to me; no moving parts.
Maybe a backdraft preventer, or natural draft inducer?

The close up is looking up from the bottom.


Is what it seems like. I have noticed them on large buildings “two to three” stories high. Tough to tell. It allows the cold damp “heavy” air to not spill into the unit when there isn’t a flame present.
However I am not a plumber, I was told that a similar device was an inducer. That was years ago. I may have been told wrong. I will watch this thread, I am curious as well.