Thank you for your question.

The purpose of this edit is to change the Yamate trunk line (山手幹線) classification from secondary to primary based on:

1. The Yamate trunk line is a 16.4km trunk road (幹線道路) as mentioned in various resources including https://kyoto-ankyo.com/column/202207yamatekannsenn.html

2. Consistency with other sections of the Yamate trunk line that are already marked as primary/trunk on OSM.

My sources are available documentation and personal observation of the area.

Does this answer your question?
Thank you.