I'm relieved to hear the support will work. There isn't a side stud to either side to attach to.
On the duct, I'm happy to say that is a 6 inch duct. When the vent was moved years ago, apparently the guy just smashed it flatter so it would fit behind the stud. I just hope they bent it out again and air tight sealed the darn thing.
I'm sorry to say I trust no one anymore with these things. I like to know what's going on.
Why people don't look things up if they're unsure or follow installation procedures diligently is beyond me. Especially when safety code is involved.