... which, I presume, among other things might mean, that it also contains an assembler, doesn't it?

On the other hand, the simple examples in Jon's pdf can be "translated" quite straightforwardly to "C" - for example the most trivial "echo" example

          ORG       0 
Loop: 
          MOV      C,P3.0 
          MOV      P3.1,C 
          SJMP    Loop 
 

would come out as something like

void main(void) {
  while (1) {
    P3^1 = P3^0;
  }
}

 

etc.

I would not go for the "Hello world" example until it's clear from the "echo" experiments, that all the related hardware is operational.

JW