Of course, it is vital information, however, it is not what the show will be focusing on. It’ll be more about the events that are to come rather than the events that have already happened.
And because of this episode, we know that they are just working to prevent it happening again. It also pins a motivation on half of the main cast. Pretty good.
If they kept the same backstory, then yeah. It’s a “the past is the past” moment. Nao has already started to move on and accept that she can’t do anything apart from look to the future.
Basically, it isn’t a big deal right now.
I like to think he’s just some kid who randomly gets called out of lessons to help them. He has to run all the way to the council room.