what does the pie symbol mean in macOS finder?

The pie symbol indicates that the element is being uploaded or downloaded to/from a server. Those elements may not be available locally.

The grayed part of the pie represents the percentage of data already transmitted so in your case as this part is very narrow it means that for each file the update has just started.

The pie symbol is a progress indicator that indicates the manipulation of a file of some kind. Since you are taking about Apple Filing Protocol (AFP), you are most likely referring to either:

• Transferring from internal to network
• Copying from network to network

It could also be:

• Transferring from a drive to another drive
• Transferring from network drive
• Copying a file
• Safari (and other) downloading from the internet
• and many more…

As @LouisLac said, this could also be uploading or downloading from iCloud.