I think this is based on a misunderstanding of what happens with naturalized Canadians, or what happens when immigrants choose to come to Canada and become citizens. It's at that moment that their citizenship is sort of set in stone, and it's from that period on that we would look at their children born abroad.
I've heard this described as these immigrants being the first generation born outside of Canada, and in fact, that's the fallacy. Their action of becoming a citizen, of choosing Canada once they come to Canada, eliminates their prior birth outside of Canada. So in that sense they are treated the same as individuals born in Canada, who become citizens from that action in Canada.