It's citing a wikipedia article, which itself has been flagged for needing a better source [0]. The wikipedia in turn cites Statista [1], which claims this is "original data" that cannot be verified without a paid account.
Additionally, the number itself seems to actually be taken from Eurostat (an actual source) [2], which helpfully defines what they mean as the 87% for Poland. Surprise, surprise, it's not actually "87% of Poles own a house". It's "87% of Poles live in households owning or renting their home". That's also conveniently missing from another headline-grabbing numbers like "16% share of housing costs to total disposable income", which refers to the total income of the entire household.
And if you want to delve deeper as for why these numbers might be what they are, you have to consider the following too:
Poland has Europe's 2nd highest share (>50%) of adults living with in their parents' home [3], with 3rd lowest average number of rooms per person [2], 2nd highest household size (number of people) [2], with one third of people living in overcrowded homes (3rd highest in Europe, vs the EU average of 16%)[2].
All this being said, I don't doubt for a second that US is much worse in this regard.
