Mask of Anthony Martinez worn as a disguise in the mission One of A Kind

I was able to wear the Golden mask of Anthony Martinez inside the tailor shop in the mission "One of a kind"

as a disguise! 47 was actually wearing the "sewer worker" outfit with the golden mask found on the shelf.

This only happened once, and I cannot recreate it. I would like to know if I managed to do something I was not

supposed to do, or was this just the games way of unlocking the mask to be worn in "contracts mode" when playing online?

Anyone got an answer please?