Your Bitcoins in Lobster Wallet are actually real. Lobster is a wallet for Stellar Network, not Bitcoin. Your transaction is not related to Bitcoin. It is related to Stellar Lumens (XLM). It is not possible to trade bitcoins in your Lobster Wallet because Lobster Wallet is designed for Stellar. For Bitcoin transactions, you need to use a Bitcoin Core wallet or a hardware wallet like Ledger or Treasure.