The answer seems to me quite simple: because they have a different coding style. Just as no one is bound to K&R or the GNU style, nothing suggests that crypto code needs to follow Linux kernel conventions.

Value consistency above everything.

Honestly, I am not convinced that the peculiar if-style isn't actually helping readability and refactoring. Note, that a Apple-style "goto break" bug might be harder to construct, when your one-line if's look like this:

   some_code;
   if (something) die(message);
   other_code;

Now the surrounding indentation does not suggest that there's an extendable block where there in fact isn't, as with Kernel style:

   some_code;
   if (something)
       die(message);
   other_code;

To be perfectly honest, the authors' style reminds me a bit of my younger self's style: keep logically connected pieces of code tightly together.

You (presumably) and I have beaten ourselves into submission to the Linux style; the authors' haven't.

On a side note: your second example even seems to suggest that the authors made some effort at additional readability by refraining from using the ternary operator construct.