I'm surprised they did the lift just 2 days before the hurricane, that's not much time to bolt everything together if they have any problems
Much of the lateral stiffness against wind on a bridge comes from the deck which of course won't be installed, the deck also adds weight which holds the bridge on the piers so it won't blow away - just bolting in the span mostly adds sail area
Or maybe they thought it was safer bolted on than just sitting on the barges
