Agreed that the description is lacking of detail but with no photos to see we have to rely on the OP's words.
So either the spoke's head has broken off enough to slip out of the hub flange's hole or the flange hole has opened up enough to allow the spoke's head to get pulled through. The VASTLY more common reason a spoke is no longer attached to the rim is that the elbow/head has broken off the spoke. As in the
#1 way spoke break. Usually there's a stub of the elbow left, but no flange/rivet like flairing about it's diameter.
But all this talk about elbows and such is assuming the spokes are the common J bend type. Again we have so little data.
Can the OP better describe the wheel? Spoke count? Rim shape? There's real reasons why many wheel builders run their wheels with far more conservative designs. So too with touring riders who are in remote areas with no support near by. With 32 or 36 spokes the rim will usually suffer less deformation when a spoke breaks. And any roadside repair is also generally easier to do with more spokes.
Some of us who have been the business for a long time have seen what just 20ish years ago were event grade components (wheels in this thread) that now are used daily by people who because they spent serious money assume the component will last longer. Andy