How does it not make sense? Are you unclear of what generation means?

Let me spell it out for you again. Generations are the measure of the change in birth rates. Gen X (or Baby busters, in Canada) only lasted five years because the birth rate picked up again after those five years, signifying a new generation.

This is also why you find different years in other countries. Just because the birth rate picked up in Canada does not mean the birth rate picked up anywhere else. The boomers were a unique exception as the end of WWII saw the USA and Canada both see an uptick in births at the exact same time.

Reading the statscan link the breakdown is different in other ways, it doesn't actually list Gen X or Millenials which may be where the confusion is coming from.

If you dig further into the website they explain that Baby busters = Generation X and Children of baby boomers = Generation Y/Millennials, but these are more American terms. We don't really use them in Canada (other than colloquially to be able to talk with Americans).