The person was named after the Saint Johann Nepomuk, a Czech Martyr. https://de.wikipedia.org/wiki/Johannes_Nepomukhttps://en.wikipedia.org/wiki/John_of_Nepomuk
In the Christian worship of saints, the bridge as an attribute to the execution of a martyr down, who was overthrown by a bridge. The most famous representative is St. Nepomuk, who is considered the patron saint of bridges.
These statues are called Bridge Saint, german "Brückenheiliger": https://de.wikipedia.org/wiki/Brücke#Bildende_Kunst