System Information
Irrelevant (I think)

Blender Version
Blender 2.81

Short description of error
The description of the error notification in the case of closing a hole with Grid Fill seems like it belongs to a different command. It tells the user to select two edge loops (like for Bridge Edge Loops tool), instead of asking the user to select a geometry with an even number of vertices (the notification shows when the selected geometry has an odd number of vertices, and so Grid Fill can't possibly close it, as it uses quads).

Exact steps for others to reproduce the error

1. Select any closed loop that has an odd number of vertices (Edit Mode).
2. Execute Grid Fill command.
3. Notification will pop up.