Hey Rescue, these are not uncommon in areas with enough, and are one of the 4 natural variants you find.
We call the white collared duchy's after the domestic ones, then there's the black, the slight slate greys and the standard brown.
All these occur in the wild without any introduction of domestic animals.
This possibly could have happened historically, but has been widespread for many decades.
(At least back 12 years before the great winter of 2009/2010 happened and reset the clock on the majority of northern rabbits).