Since when is an int a byte?

[Steven Friedrich]

I am starting a new console application using code::blocks and it gave me a main.c with hello world.
I changed the return to -1, compiled and ran it.  Here's the output in the terminal:
Hello world!

Process returned 255 (0xFF)   execution time : 0.001 s
Press ENTER to continue.

Why is it claiming the return code is a byte?  An int is 64 bits on x86_64 Linux.

[Commaster]

https://www.gnu.org/software/bash/manual/html_node/Exit-Status.html Because that's how shell and processes work?