Its about immigrants specifically leaving, which is arguably a good indicator of the desirability of living in the country.
Just like how I am not giving an opinion on the immigration/emigration policies, I'm merely offering (what I think is[2]) a correction to your post.
[1] Maybe his "correction" is wrong, but he is still only talking about stats and not policies.
[2] I could be wrong too, about my interpretation about GPs correction, but that still leaves this post void of opinions on immigration/emigration policies.
This is a place where the terminology breaks down, since technically even native-born Canadians who leave for another country are "immigrating" to that country.
I assume you mean something like: "This is about people who immigrated to Canada emigrating/immigrating a second time."
Emigrants leaving a country had been living there, perhaps for their whole life, and have decided to leave and go elsewhere.