As for Robbie Parker laughing? It looks more like a fake smile out of nervousness to me. there was absolutley no laughing. just a smile.
As for the nurse, she said no to the question if the son was ell known to have issues(because how can you know someone you dont know). Then I'm pretty sure the follow up question was "what was his mother like" and the nurse was probablly just told "the shooter mother is the kindergarten teacher here" so of course she will talk about the teacher who she knows going off bad info... I have no clue who started that claim but Im sure it was a news source trying to get a scoop and since the rest of the news didn't want to fall behind they started reporting it. Because when that news first starting to be spread there wasnt ANY info being leaked by officers other than there was a massacre.