I am guessing after hitting the tree the doors got jammed, so the driver got in the back seat to try to force open the back door or trunk access. They burned alive.
See the placement of back door emergency release in Model S: https://www.youtube.com/watch?v=01lXcD_Uz74&t=42s
Model 3 doesn't have emergency release latches for back doors.
I think Tesla tries to be too clever by far with their doors. I sure hope the rumor they are eliminating outside handles on the Cybertruck is nonsense.