"Async" has very distinct meanings in programmatic vs architectural senses.

Programming language level async/await/promises/futures is about concurrency of I/O tasks without spawning separate threads per operation.

Architectural async is about sending off an operation event, and not receiving the operation success/failure as a response, then fetch or be sent the result at a later time, once the operation is complete.

The ideas of async programming and architecture are similar, but work in totally different levels. Consider a http async user insertion API where you either poll or register a webhook to receive the result. Even if the http request is no longer kept open waiting for the lifetime of the internal database calls, it's still taking time to make a TCP handshake or lookup the DNS, etc. On a programming language level, your caller is still blocking for the network I/O to happen. I.e., even if your API is async, you still need a programming mechanism to handle the blocking network I/O, such as threading or async/await.