The way it's calculated by Stats Canada is that of 100% of the residential properties that exist, 65% of them are occupied by the family that owns the property. This can include adult children.

Basement suites are counted as a separate household, even less-than-legal ones.

That does mean that there are less than 65% of people that own a home, but you also have to account for the fact that Homeowners are FAR more likely to vote than non-home owners from a demographic perspective. The voting block is absolutely massive AND is the group that has money to fund political campaigns.