Good question !
The answer is this part of the highway is a bridge, as you can see : https://www.openstreetmap.org/way/725404687
The contributor has added informations to the highway but missed to correct the bridge. :/

According to local press (ex : https://www.estrepublicain.fr/economie/2020/09/30/mise-a-2x2-voies-de-la-rn-57-au-moins-douze-ans-de-retard) the road construction is late...

I'll fix this and try to improve a bit the overall, thanks !