I know that the devs did not build it whole and then destroy the middle, but the fact that it exists in a broken state implies that it was once whole; much like any of the buildings in the game. Post-apocalyptic means that there must have been a time before the apocalypse, or it wouldn't be 'post', i.e that the bridge must have existed complete at some point in time, in that sense it is completely irrelevant whether the devs created it whole or not; in their vision of what came before the events of the game, it would have existed complete and therefore should be able to be recreated.
Tbh I don't see why you have tried to patronise me twice for asking a valid question to the building mechanics of the game, I thought moderators are supposed to be helpful to their community, not try to drive them away to other games like when you told me in your previous post to go play Minecraft instead.