BBM:
The reason I'm inclined to believe this bit is true is because there's no real reason to lie about it.
It paints a terribly unflattering picture of his mother, for one thing.
The storyline, "Hey, my kid complained to me that he felt sick that morning, but I told him to haul his butt off to school, regardless, and oh, yeah, I didn't even bother to lay eyes on him before he walked out the door," is generally not the type of narrative a parent wants to invent if they're trying to garner public sympathy.
I do believe HD complained of not feeling well that morning.
JMO.