Apple - 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.

Technically speaking, anything that gets loaded and executed is a process; so a service is a process.

A service is a nuanced definition of something that gets loaded to provide a service like DHCP or DNS.

A alternative way to sum this up is all services are processes, but not all processes are services. An example would be Firefox, it's a process, but not a service - it's an application.