Nostr and Bitcoin are separate systems with complementary cultures. Nostr handles signed social events. Bitcoin and Lightning handle value. Together they make identity, attention and payment more directly connected.
Separate layers
Nostr does not need a blockchain to store posts. It uses relays. Bitcoin does not need to become a social network. It provides money and settlement. The combination is powerful because each layer does what it is good at.
Lightning zaps
NIP-57 zaps are the most visible bridge. A post or profile can receive a Lightning payment and the receipt can become visible in Nostr clients. That turns payments into social signals.
Wallet connect
NIP-47 adds a route for clients to interact with Lightning wallets through Nostr messages. That can make wallet-enabled social apps safer and more modular.
Crays architecture
Crays uses Nostr as the social identity and signal layer, Bitcoin and Lightning as the value layer, and Crays products as the commercial and hospitality layer. That is why the Nostr page says Nostr and Bitcoin are base architecture for Crays.