Make no mistake, they're going with that strategy because it works, and it works because the "doesn't seem upset enough" fallacy is so pervasive. During a sexual assault trial in Wales, the accused rapist's defense rested on the fact that the victim smiled and laughed before the attack. In England, another lawyer used the old "She's smiled in Facebook pictures taken since the incident, so it can't have been rape, can it?" defense.
Here's a story about a Malaysian flight attendant whose alleged rapist defended himself by saying that she was "smiling and seemed happy" afterward. There was even a point in time when Julian Assange, the Wikileaks guy, tried to defend himself against allegations of rape by showing the court smiling pictures of his victim.
The Daily Mail
On some level, everyone making that accusation has to know how strange it is, unless they're aliens wearing human skin as a disguise. You've never found yourself swimming through a shit-swamp of depression, but still smiled your way through a family member's birthday party or wedding? You've never suppressed your rage at a boss, knowing that an outburst could get you fired? Never put on a smile and acted chipper to try to defuse someone you were genuinely afraid of? Humans learn to fake emotion when they're two freaking years old. It's not much later that we learn to smile in photos.