And you, as a self-proclaimed former campaign manager, are not grasping something even more obvious.
Do you know how tightly screened the people are who sit directly behind these candidates? They are placed and then moved around for reasons of diversity and eye appeal. To believe that this guy (who is well-known to both the FBI and other security agencies who were present) simply showed up unannounced and strolled into a seat right behind her? Not only that, he was allowed to use his cell phone during the event? It's as ludicrous as saying "Yeah, I was at an NFL game last week, wandered onto the field in the second quarter, and the ball was snapped to me instead of the QB. I even threw a TD pass on the play and nobody really noticed."
If you choose to deny that this guy was known to team Grandma, I know where you can buy a privately owned and secured server used by an ex-State department official...