Cross breeding between geese is not an uncommon thing but not the norm. Take a look at the two different types of geese below and then compare the hybrid.
These are the Canada Geese.
And here is the hybrid. It seems to have the white cheek mark of the Canada Goose and lighter plumage than the Greylag, but is clearly a bit of both.
Here are some more Greylags just having fun.
There's always a real commotion when these guys come in to land