When an empty diff is retrieved from cached the (No difference) text is not shown. When first viewing the diff the text is visible.
This seems to be independent from the diff engine. I could reproduce it with wikidiff2 and the default diff. See example below:
Not shown: https://en.wikipedia.org/w/index.php?title=Sweetener_World_Tour&diff=907513441&oldid=907473226&diffonly=1
There is a html comment where "(No difference)" should be shown: <!-- diff cache key enwiki:diff:wikidiff2:1.12:old-907473226:rev-907513441:1.8.1 -->