When doing this exercise I proceeded similarly, I think, to the looping ball exercise:
- In frame 1, I set the auto keying set to Location, insert a keyframe with the object in 0,0,0
- I delete the Location Y channel in the graph editor (select channel, X to delete).
- I change the auto keying set to Available, click the Auto Keying button to activate it, move the square to the left top corner using the G key and CTRL to snap, for easy positioning.
When I do this, it inserts not just the X and Z location values, but it also inserts the Y location, the 3 rotation channels and the 3 scale channels. I removed them by hand, but why did this happen? What did I miss?
Oh I forgot to say: I'm using Blender 2.92.
Thanks in advance.
There is a hidden checkbox next to the Autokeying button:
This 'Only Active Keying Set' needs to be checked.
This is also in 2.92, but I'd recommend switching to 2.93 LTS, because 2.92 is a bit buggy especially in the rigging and animation department.