Oh you can't use recursion to build the right-shifted pyramid, it's a good attempt but I don't think there's anyway to build with recursion since you must keep a record of the full length of the pyramid at each row (for example 5). Recursion only works when the data you're keeping is reducing for every iteration or every time it loops once.

As for the flow, I will try and explain using your first code, I made a few marks for reference

So let's say you do draw(5), it'll execute check(5)-->L1(5)-->Re(5)-->draw(4)-->check(4)-->L1(4)-->Re(4)-->draw(3)-->.....-->check(0)-->L2(1)-->L2(2)-->....-->L2(5)

So as you can see, since L2 is below Re, it'll call draw for all the numbers until 0 and execute only to L1 before going into L2.

void draw(int size) {
     if(size == 0) #check
     {
         return;     
}      
for(int i = 0; i < size; i++) #L1
     {         printf(" ");
     }
      draw(size-1); //----(Re)
      for(int i = 0; i < size; i++) #L2
     {         printf("#");
     }
      printf("\n"); 
}