Both words travel without translation. Bitcoin needs none, and bank is close enough to the Spanish banco that any reader in Madrid, Valencia or Seville grasps it instantly. The hyphen separates the two words clearly, which helps when the address is spoken aloud or printed on a card. The .es ending is Spain's national domain, the address local customers expect from a provider that serves them in their own market and language.
The name belongs to the Bitcoin Bank International collection, a set of bitcoin bank addresses across several country endings. For a group already present elsewhere in Europe, it offers a natural Spanish branch address. On its own, it fits a Spanish-language neobank, a Bitcoin savings account, a custody desk for small businesses, or an education site explaining how Bitcoin banking works for households in Spain.