The city of Helsinki owns about 17% of the residential building stock, not the majority. (https://www.asuminenhelsingissa.fi/fi/content/kaupungin-omis... - in Finnish)
"And there, the Finnish capital is fortunate. Helsinki owns 60,000 social housing units; one in seven residents live in city-owned housing. It also owns 70% of the land within the city limits, runs its own construction company, and has a current target of building 7,000 more new homes – of all categories – a year"
https://www.theguardian.com/cities/2019/jun/03/its-a-miracle...
70% of land is not 70% of housing.