I am not debating whether or not sandy hook is legit I personally believe that story has more holes then a block of Swiss cheese, But do you have no personal experience with tragic loss or mourning?
Grieving is a long process and is experienced many different ways at different times for different people. I haven’t seen the CNN clip you mentioned so I can’t say that these people were grieving in the given example but that doesn’t negate the fact that people aren’t always extremely depressed when they lose someone whether that person is 100 or 6 months old.
In my personal experiences it has always been comedy and laughter that has gotten me through the death of a loved one, However I have not suffered the loss a child (experienced a girlfriend getting an abortion without my consent, still I don’t see it being the same though).
People experience loss differently and at differing intervals of time, people also present their mourning differently privately and publicly.