Either it was someone who ignorantly ran 7mm Rem Mag in a 7mm Wby Mag chamber, or it's brass from someone who forms 7mm Wby from 7mm Rem Mag cases because they cost less than half as much. These might have been culled for defects or just shot out and probably only valuable as scrap metal. I have a 257 Wby Mag, but all but 20 of my cases have "R-P 7mm Rem Mag" headstamps. They are easily formed by running a new 7mm Rem Mag case through the 257 Wby die with Imperial Sizing Wax. The shoulder comes out only partially formed, and I load them up with a known safe 257 Wby load and shoot them and out pops nicely formed 257 Wby brass, except the necks are 0.05" shorter than Wby spec, which is no big deal.
I would say those cases are scrap metal.
Mike