How can I distinguish a service form a process in Activity Monitor?
All Processes, Hierarchically

Activity Monitor can show the process hierarchy:

Activity Monitor.app > View (menu) > All Processes, Hierarchically

The grouping shows those processes launched by another process. Typically child-process will be services of the parent. On macOS many of these child processes will be XPC instances.

Services are Processes

On macOS, daemons are processes and services are processes. In your example, com.apple.audio.SandboxHelper, this is an XPC service.