it does help that he triggered the crossbows that are firing from the back.
its harder to dodge if you cant see the arrow coming right at you.
The downside though is that there does not seem to have a reload mechanism so it only works once per crossbow.
In this case it isnt attacking. Its pulling the trigger of a stationery crossbow. Similar to pulling a lever which is connected to the firing mechaism of a stationery crossbow.