My opinion was:
The primer has a distinct dent in it. Not a firing pin dent, but a dent, nonetheless.
I can't offer an opinion as to how the dent occurred. But am pretty certain the detonation happened when the primer was dented.
I doubt seriously it was S&B's fault. It traveled many, many miles getting to where it was today, and "just picking up the box" didn't cause it.
If I had to speculate, the ammo box was probably not properly handled, packed, and the entire larger box was probably slammed down on the counter, or dropped from the counter onto the hard floor beneath.
Lawyers get lied to sometimes. Not saying that's 100% sure what happened here. But something dented that primer. Ammo doesn't just detonate like that.
