You have to be careful with that statistic. It's not that 80% of Norwegians own their own home, it's that 80% live in a home that is owned someone in the household. So if you have a single parent, who owns a home, with 3 adult children living in one house, that statistic would say those 4 people have a 100% rate of homeownership. All countries measure it this way.

For example, Singapore has a rate of 91%. However, adults tend to live with their parents until they get married. They'd love to move out before that, but rents are sky high in Singapore, so people tend to just live with their parents. It's also pretty common to have multi-generation households.