If that manager was half decent he/she would have 'torn up' that report and demoted the junior, especially after accepting the extra hour and not challenging the purser at the time.
God knows what these juniors hope to achieve by reporting such trivial incidents. Maybe this crew member thinks that respect comes with the position. My only guess is that they want to become 'little hitlers' in the future. It looks like a culture issue and makes crew wary of each other watching their backs. This in turn leads to insecurity and possibly reflects on customer service.