I'd say, this is not neurotypical, but it is already obvious from dad's interview. With atypicality, one might expect unusual behaviors, but it does not mean these people are not grieving.
As to chewing gum - totally inappropriate, of course, but this is why some people hire a "social skills coach". Such coach is badly needed here, but these folks are too poor to afford him/her.
I hope there is more to the whole story than such behaviors, and that this is not the main reason the case is not yet closed. In places with better medical awareness, people are not surprised by such scenes, not at all.
Also - having read dad's post, clearly indicating learning disabilities, plus having watched his interview and now this scene, I highly doubt he'd be able to pull off a planned crime.