Bitcoin sets the topic and community describes what happens inside: conversation, events, mutual help. Together they form a phrase that needs no explanation in English and is widely understood elsewhere too. The .app ending is a generic domain ending created for applications, and it is HTTPS-only, so every connection to the site is encrypted by design. That fits a social product where members sign in and share personal details.
The name belongs to the brand category with a clear lean towards social and membership products. It suits a network of city meetups that wants one app for calendars and chats, a conference that keeps attendees connected between editions, or a creator who runs a paid membership with courses and discussion. It can also serve as the app address for an existing community whose website lives on another domain.