Hello Adrian,
it might be confusing but it isn't if you have further look at the markings.
BWB doesn't mean Bundeswehr Bund but rather 'Bundesamt für Wehrtechnik und Beschaffung'. This is the government authority which is responsible for all acquisitions, technical and electonic developments of the Bundeswehr including weapons, armour-bearer and all kind of relevant material. So this watch was acquired by the BWB from IWC for instance as a kind of prototype probably among other brands and not issued to the troops later on. The watch remained in the stock of the BWB and was later sold by the VEBEG, the company which is responsible for the selling after the decomission.
Kind regards

