Yeah, seeing the vid, I gotta go with the "shock and/or medicated" theory. Grief doesn't always show up as obvious sadness, and it's not a consistent thing, either- it comes and goes in waves. Losing a child is one of the most devastating things a human being can experience- in any way, and this was a particularly horrific one. It wouldn't be at all surprising for his emotions to be everyplace, or for him to be numb, or for him to not even really feel like it's "real" for awhile.
That he's not crying doesn't mean he doesn't have depth of emotion. That his response not being to cry or look sad in one particular moment in time is taken as a sign of lack of emotion is more than anything else a sign of how culturally fucked up we are when it comes to grief. There's an expectation that we're supposed to be sad for a month straight and then be fine. That's insane and not at all how it works for the vast, vast majority of people and losses.