Doubt it was fitted by the dealer... but I'd guess it is probably a more recent addition. 15 years ago or so a bunch of them (NOS) surfaced on ebay. Don't know the back-story, but for a while there were a lot of them available... they may have been a part of that west coast cargo-container stash that the Sandy Bandit forgot about and got bought up at an auction? They didn't sell like hotcakes, and so most went pretty cheaply. Seemed like most (of that batch anyway) were for BSA unit singles, but I do recall seeing some for Triumph twins.
I admit I did actually think (for a moment) about buying one for a fast fix/flip on a roller, but even a $25 price tag couldn't convince me to do that to it.