Earlier quoted context omitted.
News flash: A transaction requires a buyer and a seller. If you bought Bitcoin, someone else sold Bitcoin.
That doesn't account for an imbalance in the number of potential buyers and sellers. It's very easy to buy a house for $100 million. Go to your real estate agent and say "Here's a $100 million. Buy me a house." It is, however, considerably harder to sell a house for $100 million.
The only reasons it is different with houses is because people are emotionally invested in them, not all houses are equivalent (and thus their value is unique per house), and liquidity is hence really low, and market prices adjust slowly.
Bitcoins are worth a thousand dollars because people who own them are not willing to part with them for less, and people who are buying them are willing to pay that much. This is economics 101. You can always cash out at the market price, unless liquidity is low; the only time that happens is in a teeny market or a crash.