My thought is that the part was from another, similar movement, where the bridge was harshly cleaned. The nickel plating looks damaged, showing the brass underneath.
Either way, it's a bit of a frankenwatch.
gatorcpa
That was my first thought, except you can still see traces of the plating (probably rhodium) on the "golden" bridge.
Strange.
Perhaps this golden bridge was done by purpose at the factory. There are other movements from Girard Perregaux with two coloured bridges on automatic movements.