500k on 100k income? The rule of thumb for banks in Denmark is to take your yearly income (before tax) and multiply it by four, and that’s what you’re allowed to borrow. So your friend is over-indebted by Danish standards.

As a foreigner, banks would’ve been very reticent about giving him a bank loan, and he would’ve had to down-pay at least 20% of his mortgage.

In other words: I find your friend’s case extremely unlikely and probably made up.

FYI: most people’s expenses go _down_ by buying in Denmark. The interest rates are stupidly low, in some cases even negative, you can pause principal reimbursement for 10 years, and your tax rate goes down.