If I understand the "Design Standards" Microsoft publishes, the "busy" is related to the window. Working in background pointer, is when something is working in the background on the client. I tried to force windows to show me various pointers using client-side and server-side actions. But all I ever see are the 2 pointers shown here. I couldn't tell the difference between a server delay and client delay. Though if it was my client delaying, often the circle would stop annimating.
The following table shows pointers that users see when performing an action that takes longer than a couple of seconds to complete.
Shape Name When used Busy pointer Used to wait for a window to become responsive. Working in background pointer Used to point, click, press, or select while a task completes in the background.