In order for inflation alone to account for $300,000 delta in value they'd be spending so much on these houses that they would be fine financially by almost any metric.
It's well, well above the rate of inflation.
Official inflation from 2015 to 2024 was around 33%. If the house cost 1mil, then the entire appreciation of 300k was due to inflation. If the house cost 500k - over half of the appreciation was due to inflation.