Unable to interpret control operator in linux

I have the following C program saved in a file named 1.c

#include<stdio.h> void main() { printf("Hello World");}

After compiling it, I try to execute it using

./a.out || echo Hi

I expect to see the following output

Hello World

But the output that I get is

Hello WorldHi

The above output seems to be wrong since echo hi should execute only if ./a.out does not get executed successfully. Where am I wrong in interpreting the output?