That was really dumb. For one, the .500 Nitro is a dangerous game rifle, so for who in the heck would you make a single shot dangerous game rifle?
.500 Nitro is whatever you want it to be. ...just like .30-06 is whatever you want it to be.
If every cartridge were reserved only to be used for its original purpose, .30-06 would only be a military cartridge. And, where would we be without it?