Quick back of the envelope calculations: 50 years times 12 months times 500 euros rent (estimate, in 2018-euros, of their subsidized rent) is 300k that they have spent on their house that has a current value of probably 200k or so, and still is 0% theirs...
Mortgage often costs more per month than rent. If you invest the difference (which they probably didn’t) renting can be cheaper even in the long term. Plus you have less risk and more freedom. It really depends on a lot of factors and the math is not as simple as in your calculation.
I found that for me buying would be a financial loss if it cost more than 150k€, and this doesn’t even include additional commuting cost. Good luck finding anything larger than a broom cabinet for that price.
I'm living quite happily in a broom closet that's currently valued at around 150k, 130 when we bought it. Terraced home, 75m2, 60 m2 garden, 3 bedrooms, €300 mortgage, very central location in a big city in NL. We were very lucky, but these kind of gems can still be found every now and then.
If you haven't spent 20 years on a social housing waiting list it's hard to find places with a rent lower than your mortgage would be though. Studio's and one bedroom apartments in my city can easily cost €800-€1000. That's what you'd pay for a 250-300k mortgage.
We paid €800 (incl. utilities, excl. taxes) in 2011 for the top floor of a single family home and the only reason our rent didn't rise from that is because I threatened the landlord to call in the local council to check if it was safe to live in. The single best financial decision we have ever made was to move from there to our current place. We broke even within 2 years and a year from there we're €10k ahead compared to our previous home.
I recently did advise a friend to stay in her rented home: large terraced home, they've put in quite a lot of work so it's really lovely, they have a large garden, nice neighbours, one of the nicest streets in town. They pay €400 or something. Similar homes are 300k in their town. They're a single income family and if you live in social housing your rent is subsidized when your income gets lower. I don't see why they would take the risk of buying when they're in such a good place now. They're on the fence, they love their current home but their parents tell them they "should" buy. I wouldn't do it if I was her - or at the very least, save up a lot of cash and wait until the next downturn.