The definition was not established for the purposes of enumeration, but rather so that a citizen could come before their ministry of education or their school board to say that they are entitled to education in the language of the minority and claim that right. When someone comes before their school board, it is relatively easy to check their background, have a discussion with them and understand their situation.
Evidence of meeting #73 for Official Languages in the 42nd Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was questions.
A recording is available from Parliament.