For various reasons, that number changes drastically over time, and rules to live by change. Just 20 years ago, interest rates were over 10%, and housing prices were lower to accommodate. So someone coming out of that time frame may tell their children "make sure your house is only 2x a year's gross salary".

Side note: it's interesting to watch...after inflation, the final cost of houses hasn't changed much in the past twenty years.

Example: you have a house that costs $100,000 with a 10% rate. After 30 years you pay $315,929.09

But today, that house has doubled in value to $200,000, and someone buys it with a 4% rate. After 30 years, they pay $343,735.91.

I only illustrate that to say, yes, twenty years ago it only had to be 2x. Now it has to be 5x. If interest rates went back up to 10%, then the value of that house would most likely drop back down to $100,000 because people wouldn't be able to afford it unless it came down to that price