What's the big deal???
All that happened was a 7mm Wby Mag was FIREFORMED to a 7mm Rem Mag. No big deal.
It happens all the time when folks fireform cases from original to the Ackley Improved versions.
I had a 30-06 that had been improved by the late Austin Moorcroft, by straightening out the case taper to ONE degree and pushing the new 40 degree shoulder ahead so that the neck was .250 in long.
It gave a substantial increase in velocity as well as recoil, when loaded to its full potential. Too much for me, so I sold it to a fellow that insisted recoil didn't bother him.
If the shooter was shooting factory cartridges, which are usually very close to minimum dimension spec, I'm willing to bet that cartridge chambered without any resistance at all.
They both headspace on the face of the belt as well, which are identical. SAFE TO DO. Smart, maybe not, considering the expense of the Wby cartridges.