We will never know what happened.
I can tell you this though, having your kite leash hooked up with the QR on the bar side, and not your side, is a death trap should you release the kite and it is looping. I know this from when leashes did not have QRs and getting worked bad once.
Also, watching Bill (tennis Bill) a couple months ago in the same scenario was pretty overwhelming.
No one is strong enough to "reel in" the kite on the leash. It's a death trap, for certain when in reasonable wind with a looping kite.

It's an easy fix, just make sure it is attached properly.

Not to be a nanny, but I think most people underestimate how bad things can get. Most of the time, things are functioning normally and kiting seems more safe than chewing gum.
That could not be further from the truth. When lines break or a bridle snaps or gets caught, these kites basically do all they can to whack you (quickly) and most times you won't get a second chance at avoiding serious injury, or worse.

Knowing your safety systems is crucial to not eventually getting hurt really badly.
Keeping a safe distance so that when things do break you have time to react is crucial.
Still, most people won't do either. (Just putting up facts, do with as you wish).