Thank you for raising this interesting topic, Neeta Bhansali.
I think the explanation is that in the compare revision view, time stamps are rounded to the full second, whereas timing corrections can be of a fraction of second. Hence the red dotted line to indicate such fractional timing changes.
I just have a question about the "Compare Revisions' tool of Amara.
When I see the compare sheet there is a red dotted line around the timing of some subtitles in the new version even though the timing is exactly same and there are no changes.
What is the meaning of those dotted lines?
I have attached a screenshot below