Isn't this obvious? Anyone who was old enough to remember 9/11 whom I've spoken to can recall several mundane aspects of that day.
The subtitle addresses this:
BU study finds memories of mundane incidents can be
strengthened when they get attached to a memory of an
emotionally charged event[0]
So doesn't seem that obvious at all.
I remember random mundane events from tons of random days, unconnected to any prominent event (as near as I can determine anyway). And I also remember some random mundane stuff from days something prominent did happen. Whether there's a bias towards days with prominent events is entirely unclear to me.