Your first pic from DuraVent say “the connections maybe be further secured” This is not a requirement, you know this.
Your second pic is either outdated or came from larger b-vents installation instructions. This is the current b vent instructions for Metal Fab sizes (3"-14"):
If the b vent in the OP pic was properly supported, I would not call out missing screws – we don’t have 100mph winds inside our attics here. If tornado makes a landing inside that attic, the screws won’t do much good anyway. As you know, the liability here is high, if it was common for these b vents to come loose, they would all indeed require it.