Although the browning in it may be because of a result of other similar species, not white fronted, in breeding range.
Likely not a Domestic cross, other factors such as size would be present. we rasied a bunch of geese as kids, and had Canada crosses every other year or so that were much different.
My guess is 2 separate wild species.
Not uncommon for them to mate and create offspring, but is pretty rare for them to survive long enough to get shot. The crosses usually get picked off as young, do to them standing out like a sore thumb in a crowd.
Excellent trophy.