well, they believe it really happened, and that's all we (and they) have: belief
like I said, it's be easy to fake this, so I guess they must trust whoever reported it to them. The data could be totally correct, but the person reporting it could have known about the bug, and stole the money from themself, then presented the thief as a 3rd party when in fact they "stole" their own money.
not seen the details, so I have no info as to how much was lost
As I said someplace else. It was known and discussed informally by a small group @ DefCon back in early August.
However since:
(a) I really didn't pay attention to it
(b) everyone I mentioned it to after accused me of FUD
(c) since it was just a bunch of people sitting around drinking & talking at a bar I had no proof said conversation ever happened.
(d) I really didn't understand the attack (did I mention drinking at a bar)
(e) the amount of funds I have on my lighting node won't buy 2 cups of coffee so even if all the of lightning network crashed it and I lost all of it, it would be a zero event for me at the end of the day.
I didn't follow up on it.
So there was more then 1 person who knew about it so it's a safe bet someone did something. That's just human nature.
As to how much. I doubt it was that much or there would be discussions about it. But that's just my opinion.
-Dave