For a vest to work, it actually performs best if you're wearing it, or have it around a pig carcass or something. It doesn't really matter if you shoot it with FMJ or lead bullets. Even a IIA vest will stop pedestrian 9mm. That vest didn't look to be properly fit or in the best of shape, so they probably got it off Ebay. That would make it rather dicey, but... eh... at least they know that one worked.