[SPARK-48027][SQL][FOLLOWUP] Add comments for the other code branch

[beliefer]

What changes were proposed in this pull request?

This PR propose to add comments for the other code branch.

Why are the changes needed?

https://github.com/apache/spark/pull/46263 missing the comments for the other code branch.

Does this PR introduce any user-facing change?

'No'.

How was this patch tested?

N/A

Was this patch authored or co-authored using generative AI tooling?

'No'.

[beliefer]

ping @AngersZhuuuu cc @cloud-fan

[cloud-fan]

thanks, merging to master!

[beliefer]

@cloud-fan Thank you!