It's really, really complicated.

There are two basic principles for recognizing citizenship: jus soli (being born on a country's territory) and jus sanguis (being the child of one or more citizens). Countries differ in which of those they accept and to what extent. Canada recognizes jus soli always, but jus sanguis only under limited circumstances, and the exact rules for claiming citizenship here via jus sanguis have changed recently.

It's possible for a child of two people from countries that don't recognize jus sanguis (or who are stateless themselves) who was born in a country that doesn't recognize jus soli to have no citizenship by birth at all. This is particularly a problem for refugees, but can happen to just about anyone from any walk of life.

Under the current law, a Canadian citizen born abroad can't pass Canadian citizenship to their own child via jus sanguis anymore, although the rules were looser thirty years ago. The child is still a citizen if born inside Canada (jus soli), but the subject of the article linked in the opening post was born abroad.

The number of stateless people in the world apparently numbers in the low millions at present. It is a big issue.