Don’t know but either way it’s near impossible without practice for a 6 year old to do something like this by himself. You could see the tethers in teh video. They weren’t made to be long enough to wrap to a pole then back to the center of the balloon so they could be centrally controlled. So as soon as one gets untied the thing goes sideways. They’d have to be untied at about the same time or it would go sideways and then he’d have to climb in with the balloon sideways and then somehow untie the other tether.
Just doesn’t sound plausible to me.
Here’s what I think:
Supposedly, the balloon was tethered in the family’s backyard. The neighbor reports that the two brothers were up on the roof with cameras and that they obviously believed that their brother was inside the balloon.
That sheds some light on this, I think. Maybe they talked their baby brother into the balloon, untied it, and got out their cameras to see what happened.