im sure the huge short position is tied to Wallbridgebeing added to the the GDXJ.
Seems to me that the GDXJ must have acquired the shares from short-sellers because there's no way they acquired those shares legitimately on the open market. In my opinion, they shorted the stocks to themselves..... They shorted at the high, and when the GDXJ rebalances (offloads Wallbridge), the shorters will make their profit.
it's convoluted, but i am sure that this is how they schemed to profit