By being valued at 12 Bitcoins. That means the house has outperformed Bitcoin.

When the house was bought:
1 Bitcoin = $100k
1 house = 10 BTC = $1m

After 2 years
1 Bitcoin = $200k
1 house = 12 BTC = $2.4m

That means the house has outperformed Bitcoin. Even if there's no dollar in the world anymore, the house will have outperformed Bitcoin if the exchange rate is 12 BTC instead of 10