That's the point it looks like he should have pulled back and bailed.
Precisely, that's what he did, just one second after the first split. But with the step slope, he had some troubles to bail out.
The trunk began splitting like barberchairing but you are right with the word "disintegrating", the whole thing collapsed. Scary !
My guess is that he was aware of something could possibly turn wrong, or he wouldn't react so rapidly.
A defect showing outside can be read, but what about its extend inside and the remaining strength (or actually lack of strength)?
I do know that the faller's security books say "in doubt, don't do it". I don't speak for the idiots who will do it blindly, no matter what, but for the experienced faller, I guess it's a matter of confidence and mitigating the risks.
Like this other one:
<iframe width="560" height="315" src="https://www.youtube.com/embed/-GyZpEUDOts" frameborder="0" allowfullscreen></iframe>
The defect is obvious, far less is its effect on the trunk integrity.